Earthing and shielding of a stator of an axial flux machine

Abstract

This invention relates to an electric machine having a shielding structure (1) for reducing a capacitive coupling and / or earthing, in particular an electric synchronous machine, wherein the electric machine has a rotor (3) and a stator (4), wherein the stator (4) has stator teeth (5) on the outer circumference of which windings (6) are arranged, wherein the shielding structure (1) is formed by a pole shoe structure (7) arranged on the stator (4) or on the rotor (3) and is coupled to a housing of the electric machine (2) or to the earth of the electric machine (2), wherein the pole shoe structure (7) and / or the stator tooth (5) are / is coupled to an earthing wire (8, 9) for forming the earthing with the earth of the electric machine.

Description

[0001] Grounding and shielding of a stator of an axial flux machine

[0002] The invention relates to an electric machine / electrical machine with a shielding structure for reducing capacitive coupling and / or grounding, in particular an electric synchronous machine, wherein the electric machine has a rotor and a stator, wherein the stator has a plurality of stator teeth, on the outer circumference of which windings are arranged, wherein the shielding structure is formed by a pole shoe structure arranged on the stator or on the rotor and is coupled to a housing of the electric machine or to the ground of the electric machine.

[0003] Variable-speed drives are operated using frequency converters. The frequency converter generates a three-phase AC supply voltage from the DC voltage. To generate this three-phase AC voltage, an arrangement of B6 bridges with six semiconductor switches is used. These semiconductor switches convert the voltage into a three-phase AC voltage using a pulse pattern and pulse width modulation. Since smoothing of this generated voltage via the motor inductances is only partially achieved, a common-mode voltage is generated at the machine star point. The common-mode voltage is thus a result of the converter's pulse width modulation. Due to the capacitive coupling in the motor, high-frequency voltages are generated in the rotor shaft, primarily via the capacitive coupling paths to the rotor shaft. These high-frequency voltages induce bearing currents, as these voltages are dissipated via the ball bearings.Currents in the ampere range cause the process of electrical erosion between the balls and bearing shell.

[0004] This process leads to bearing damage, significantly reducing their service life. In addition, conductive components that have a low-impedance electrical connection to the shaft, such as the transmission gears, are also damaged. The effect of capacitive displacement currents, along with the effect of inducing shaft currents, leads to increased EMC radiation in the motor. To prevent the formation of capacitive displacement currents, the capacitive paths in the motor should be blocked wherever possible. To achieve this, both grounding and shielding measures are required.

[0005] The influence of stator grounding is essential to eliminate capacitive currents between the stator and the housing. The path between the stator and the housing has a dominant influence in the voltage divider. To achieve this, the stator and all its components must be connected to the general motor ground reference point with as low a resistance as possible.

[0006] It is known from the prior art that in radial flux motors, grounding is generally achieved via a low-resistance connection without the need for additional measures. This low-resistance connection is achieved because, in a classic stator design, the stator teeth and the stator yoke are usually manufactured as a single piece. Furthermore, in radial flux motors, the motor stator is usually integrated into an electrically conductive housing in such a way that a low-resistance connection between the stator yoke and the housing is possible. This assumes that the air gap provides a low-resistance connection between the stator and the housing, and that this provides good grounding for the stator.

[0007] With axial flux motors, special measures must be taken to ensure the stator and all its components are grounded. This is related to the design of the axial flux motor. In principle, two different designs for axial flux motors can be found in the literature. In one design, the two rotor disks are positioned on the outside, with the stator disk in the center. In another design, however, the rotor disk is positioned on the inside, and the two stator disks are arranged on the outside.

[0008] A design of an axial flux motor with a configuration in which two rotor disks are designed on the outside, with the stator disk positioned in the center, is described in WO 2020 / 229 399 A1. This configuration shows the stator teeth guided by a plastic holder. The stator teeth are mounted on a stator core and positioned using a plastic structure. Pole shoes made of SMC (soft magnetic composite) material are mounted on the laminated stator teeth at both ends.

[0009] It is therefore an object of the present invention to provide a space-saving contacting and earthing of the stator in axial flux machines as well as a shielding structure as shielding of the axial flux machine to reduce the capacitive couplings.

[0010] This is solved according to the invention by the subject matter of claim 1.

[0011] This is achieved according to the invention in that the pole shoe structure and / or the stator tooth are coupled to the ground of the electrical machine, in particular the electric axial flux machine, with a grounding wire to form the grounding connection. In a particular embodiment, the pole shoe structure and the stator tooth are each connected to the ground of the electric machine / electric motor via a (separate) grounding wire. Of course, in the absence of a pole shoe structure, the grounding solution is implemented by the presence of only one grounding wire to connect the stator tooth to the ground of the electric machine.

[0012] It should be noted that the axial flux electric machine is an electric machine with at least one stator and at least one rotor. The at least one rotor and the at least one stator are arranged opposite one another in an axial direction, ie, in a direction of a rotational axis of the axial flux electric machine, such that an axial air gap is formed between the at least one rotor and the at least one stator in the axial direction.

[0013] This significantly minimizes the capacitive coupling of the stator winding to the housing through direct and very space-saving contact with the stator tooth sheet contour. In addition, a shielding structure on the tooth tip or on the pole shoe can be achieved using a pole shoe structure, which also requires minimal space to contact. Both the space-saving contact to the stator tooth and the contact to the shielding structure must be connected to the general reference ground of the system. In other words, the invention relates to suitable and, if possible, space-saving contact (e.g., a wire contact) and grounding of the main components of the stator to a general reference ground. The general reference ground refers to the ground point that forms the overall ground point of the system and to which the ground connection of the frequency converter and thus the general ground to which all other motor components are referenced.The contact to the general motor ground can be made by a separate ground wire at the motor terminals, a ground strap or by a conductive connection to the screwing points of the stator on the outer housing, which in turn is conductively connected to the general reference ground.

[0014] The advantage of the invention is that the shielding through the clever solution approach in the stator tooth reduces the capacitive coupling paths between the winding and the rotor and thus reduces the voltage transmitted to the rotor shaft.

[0015] Advantageous embodiments are claimed in the subclaims and are explained in more detail below.

[0016] Advantageously, the stator tooth is designed as a laminated stator tooth or a sheet metal stator tooth, so that iron losses are reduced.

[0017] The pole shoe structure preferably has conductive tracks / conductor tracks on its surface, as well as an insulating layer. The insulating layer is arranged on the inside of the pole shoe structure, i.e., the side facing the stator.

[0018] Preferably, the ground wire of the pole shoe structure is arranged in a groove on the pole shoe surface. For contacting the reference ground point, contact is thus made via a wire located in a small groove on the pole shoe surface. Shielding is achieved through the design of the conductor tracks and the grounding of the pole shoe structure. This reduces the capacitive coupling between the winding and the rotor. This results in a reduction in the voltage coupled to the rotor shaft.

[0019] The stator windings preferably have insulation and preferably a ground wire arranged in a groove inside the pole shoe structure. In other words, the preferably laminated stator tooth is guided under the winding or winding insulation via a suitable contact along the laminated structure in a stator groove, which is connected to the reference ground point. A suitable winding chamber or groove is required to route the contact. This groove is designed as a small recess in the inner part of the pole shoe structure.

[0020] This ensures an ideal connection of the stator components to the common reference ground point, short-circuiting parasitic capacitances between the stator tooth and the housing. This results in a reduction in the voltage coupled to the rotor shaft.

[0021] The electric machine preferably has a rotor-stator-rotor arrangement or a stator-rotor-stator arrangement. In the first-described arrangement, pole shoe structures are generally fixed to the laminated stator teeth on both sides. The pole shoe structures serve to conduct the stator flux. In the second arrangement, pole shoe structures in the form of stator shoes are generally located on only one side.

[0022] Advantageously, the electric machine in the stator-rotor-stator arrangement has an additional stator yoke on which a plurality of stator teeth are arranged. The preferably laminated stator teeth are directly connected to the stator yoke on the side opposite the stator shoes. Consequently, the laminated stator teeth are wound separately and subsequently applied to the stator yoke depending on the configuration. The stator yoke preferably has an additional ground wire, which is connected to the central ground of the electric machine. Thus, suitable contact for the stator yoke is realized along the laminated design, e.g., in a stator slot, which is connected to the reference ground point.

[0023] The previously described features for grounding the stator teeth can also be used equivalently without pole shoes.

[0024] The invention is explained in more detail below with the help of a drawing.

[0025] They show:

[0026] Fig. 1 is a schematic representation of an electrical machine according to the invention with a shielding structure according to a first embodiment;

[0027] Fig. 2 is a detailed view of a shielding structure of an electrical machine of the first embodiment;

[0028] Fig. 3 is an exploded view of the detailed view of a shielding structure of an electric machine of the first embodiment;

[0029] Fig. 4 is a schematic representation of an electrical machine according to the invention with a shielding structure according to a second embodiment;

[0030] Fig. 5 is a detailed view of a shielding structure of an electrical machine of the second embodiment; and

[0031] Fig. 6 is an exploded view of the detailed view of a shielding structure of an electrical machine of the second embodiment.

[0032] The figures are merely schematic and serve solely to clarify the invention. The same elements are designated by the same reference numerals.

[0033] Fig.1 shows a schematic representation of an electrical

[0034] Machine 2 with a shielding structure 1 according to a first embodiment. Shown is an electric machine 2 in a stator-rotor-stator arrangement. This means that the electric machine 2 has a rotor 3 arranged internally on a rotation axis 16, with a rotor disk 19, and rotor magnets 8 arranged on the rotor disk 19. The stator 4 is arranged on both sides of the rotor 3. The stator 4 and the rotor 3 are spaced apart from one another by an air gap defined between an outer contour of the stator 4 closest to the rotor 3 and an outer contour of the rotor 3 closest to the stator 4. The stator 4 has a stator yoke 14 on its axially outer side, which is arranged on a motor shaft 17. Stator teeth 5, which can be formed as laminated or sheet-metal stator teeth, are arranged on the axially inner side of the stator yoke 14.Windings 6 are arranged on the outer circumference of the stator teeth 5, which in turn can have winding insulation. A pole shoe structure 7 is arranged on the axially inner side of the stator 3, i.e. the side of the stator 4 facing the air gap. The pole shoe structure 7 forms the shielding structure 1 and thus shields the stator 4 from the air gap, thus reducing capacitive coupling of the electrical machine 2. In a slot 12 (shown in Figs. 2 and 3), which is designed as a stator slot 12, there is a grounding wire 8 for grounding the stator 4, which is coupled to the effective ground or the housing of the electrical machine 2. Furthermore, the stator yoke 14 is also assigned a grounding wire 15, which is also arranged with the effective ground of the electrical machine 2.

[0035] Due to this arrangement, the shielding structure 1 and the clever solution approach in the stator tooth 5 reduce the capacitive coupling paths between the winding 6 and the rotor 3 and thus reduce the voltage transmitted to the rotor shaft.

[0036] Fig. 2 shows a detailed view of a shielding structure 1 of an electrical machine 2 of the first embodiment. The stator pole shoe structure arrangement illustrated in Fig. 1 is shown. The same components are provided with the same reference numerals. In particular, Fig. 2 shows the stacked or laminated stator tooth 5, on which the windings 6 are arranged. The pole shoe structure 7 has a groove / pole shoe structure groove 13, into which a ground wire 9 of the pole shoe structure is guided. The ground wire 9 is also connected to the effective ground or the housing of the electrical machine 2, thus grounding the pole shoe structure 7.

[0037] From the exploded view of the detailed view of a shielding structure 1 of an electrical machine 2 of the first embodiment in Fig. 3, it is clearly visible that the pole shoe structure 7 has conductor tracks 10 on its surface facing the air gap and thus the rotor 3. Shielding is achieved through the design of the conductor tracks 10 and the grounding of the pole shoe structure 7. This reduces the capacitive coupling between the winding 6 and the rotor 3. This results in a reduction in the voltage coupled to the rotor shaft. An insulation 11 of the pole shoe structure 7 is arranged between the pole shoe structure 7 and the stator 4.

[0038] Fig. 4 shows a schematic representation of an electrical machine 2 according to the invention with a shielding structure 1 according to a second embodiment. An electrical machine 2 in a rotor-stator-rotor arrangement is shown. This means that the electrical machine 2 has two rotors 3 arranged externally on a rotation axis 16, each with a rotor disk 19 and rotor magnets 18 arranged on the respective rotor disk 19. The stator 4 is arranged within the rotors 3. The stator 4 and the rotor 3 are spaced from one another by an air gap defined between an outer contour of the stator 4 closest to the rotor 3 and an outer contour of the rotor 3 closest to the stator 4. The motor shaft 17 is arranged on the axially outer surface of the rotor disk 19. In contrast to the first embodiment shown in Fig. 1, the embodiment shown in Fig.4 in that the stator 4 does not require a stator yoke 14. The embodiments also differ in that pole shoe structures 7, each designed as a shielding structure 1, are arranged on both sides of the stator tooth 5. This again shields the stator in the air gap towards the rotor 3, so that the capacitive couplings are reduced. The detailed design of the pole shoe structures 7 and of the stator 4 corresponds to the design according to Figures 1 to 3. The only difference is that pole shoe structures 7 according to Figures 5 and 6 are arranged on both sides of the stator tooth 5. Insulation 11 is introduced between the pole shoe structures 7 and the stator teeth 5.

[0039] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two (e.g.) similar features without establishing a priority.

[0040] List of reference symbols

[0041] 1 Shielding structure

[0042] 2 electric machine

[0043] 3 Rotor

[0044] 4 Stator

[0045] 5 stator teeth

[0046] 6 windings

[0047] 7 Pole shoe structure

[0048] 8 Ground wire stator

[0049] 9 Ground wire pole piece structure

[0050] 10 conductive tracks

[0051] 11 Isolation

[0052] 12 Slot / stator slot

[0053] 13 Groove / pole shoe structure groove

[0054] 14 Stator yoke

[0055] 15 Ground wire stator yoke

[0056] 16 Rotation axis

[0057] 17 Motor shaft

[0058] 18 rotor magnets

[0059] 19 Rotor disc

Claims

Claims 1. An electric machine having a shielding structure (1) for reducing capacitive coupling and / or grounding, in particular an electric synchronous machine, the electric machine having a rotor (3) and a stator (4), the stator (4) having stator teeth (5) on the outer circumference of which windings (6) are arranged, the shielding structure (1) being formed by a pole shoe structure (7) arranged on the stator (4) or on the rotor (3) and being coupled to a housing of the electric machine (2) or to the ground of the electric machine (2), characterized in that the pole shoe structure (7) and / or the stator tooth (5) is coupled to the ground of the electric machine by means of a grounding wire (8, 9) for forming the grounding.

2. Electric machine according to claim 1, characterized in that the stator tooth (5) is designed as a laminated stator tooth or a laminated stator tooth.

3. Electric machine according to claim 1 or 2, characterized in that the pole shoe structure (7) has conductive tracks (10) on its surface.

4. Electric machine according to one of claims 1 to 3, characterized in that the pole shoe structure (7) has an insulation (11).

5. Electric machine according to one of claims 1 to 4, characterized in that the earthing wire (9) of the pole shoe structure (7) is arranged in a groove (13) on the pole shoe surface.

6. Electric machine according to one of claims 1 to 5, characterized in that the windings (6) of the stator (4) are provided with insulation.

7. Electric machine according to one of claims 1 to 6, characterized in that the earthing wire (8) of the stator (4) is arranged in a groove (12) in the interior of the pole shoe structure (7).

8. Electric machine according to one of claims 1 to 7, characterized in that the electric machine (2) has a rotor-stator-rotor arrangement or a stator-rotor-stator arrangement.

9. Electric machine according to one of claims 1 to 8, characterized in that the stator (4) in the stator-rotor-stator arrangement of the electric machine (2) has an additional stator yoke (14) on which a plurality of stator teeth (5) are arranged.

10. Electric machine according to one of claims 1 to 9, characterized in that the stator yoke (14) has an additional earth wire (15) which is connected to the central mass of the electric machine (2).

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