Electric machine having a shielding structure for reducing capacitive coupling in same, and an axial flow machine having the shielding structure

Abstract

The invention relates to an electric machine having a shielding structure (1) for reducing capacitive coupling in an electric machine (2), in particular an electric synchronous machine, wherein the electric machine has a rotor (3) and a stator (4), wherein the stator (4) and the rotor (3) are spaced apart from one another by an air gap (5) defined between an outer contour of the stator (4) located closest to the rotor (3) and an outer contour of the rotor (3) located closest to the stator (4), and the stator (4) has winding heads (6), wherein the shielding structure (1) is coupled to a housing (7) of the electric machine (2) or to the ground of the electric machine (2), characterised in that the shielding structure (1) is located in the air gap (5) and / or the shielding structure (1) encloses the winding heads (6) of the stator (4).

Description

[0001] Electric machine with a shielding structure to reduce capacitive coupling in it and an axial flux machine with the shielding structure

[0002] The invention relates to an electric machine with a shielding structure for reducing capacitive coupling in an electric machine, in particular a synchronous electric machine, wherein the electric machine has a rotor and a stator, wherein the stator and the rotor are arranged spaced from one another by an air gap defined between an outer contour of the stator closest to the rotor and an outer contour of the rotor closest to the stator, and the stator has winding heads, wherein the shielding structure is coupled to a housing of the electric machine or to the ground of the electric machine. The invention further relates to an axial flux machine with a shielding structure according to the invention.

[0003] The development of electric drives is increasingly focused on efficiency, with the greatest potential lying in improving inverter technology. Meanwhile, improving power module technology presents significant technical challenges. Increased parasitic currents in the system are one of these challenges, which not only poses problems for electromagnetic compatibility (EMC). These parasitic currents also cause various types of bearing currents, which can lead to reduced bearing life and ultimately premature system failure.

[0004] A distinction is made between three types of bearing currents that can occur in inverter-fed electrical drive trains: electrical discharge currents (EDM), circular currents, and rotor-to-ground currents. The cause of all these currents is the inverter, which does not provide continuous voltage levels to drive the motor. The switches in the inverter's power module only jump between the voltage levels (+ and -) of the battery to generate sinusoidal currents. This switching method creates a common-mode voltage, which is responsible for the bearing currents. This shaft voltage causes an electric field between the rotor and the stator, or ground. Due to these capacitive couplings between the stator windings and the rotor shaft, voltage potentials arise on the shaft of electrical machines.These voltage potentials lead to spark discharges in the bearings and to leakage currents through the bearings, which can destroy the bearings.

[0005] Measures against spark discharges and bearing currents are already known, such as grounding the rotor shaft using special contact brushes, insulating the bearings, e.g. using ceramic balls, or insulating the inner or outer rings of the bearings.

[0006] Another measure is the integration of electrical shielding, which is known from DE 10 2017 208634 A1. In a radial flux machine (RFM), the determining capacitance between the winding and the rotor shaft is formed by the copper conductors in the winding slots. Therefore, DE 10 2017 208634 A1 describes a slot closure in the form of a cover slide with integrated electrostatic shielding between the copper conductors in the winding slots and the rotor to reduce shaft voltages.

[0007] In an axial flux machine (AFM), especially in a design with rotors with plastic supports that electrically insulate the magnets from the rotor shaft, the capacitance distribution is significantly different than in a radial flux machine. The decisive capacitance between the windings and the rotor shaft is determined by the radially inner winding overhangs.

[0008] The plastic rotor carrier, which electrically insulates the magnets from the rotor shaft, creates an additional capacitance in series with the winding-rotor capacitance. Since the rotor-shaft capacitance is usually very small due to the geometry, the effective capacitance between the winding and rotor is also very small due to the series connection. The winding conductors in the winding slots therefore have only a very small influence on the shaft voltage. Due to the spatial proximity of the radially inner winding overhangs to the rotor shaft, they create a capacitance that is significantly larger than the capacitance described above between the conductors in the winding slot and the rotor shaft. This is therefore decisive for the shaft voltages and must be taken into account with regard to bearing currents, etc.

[0009] The object of the invention is therefore to provide an improved reduction of capacitive couplings in order to overcome the disadvantages of the prior art. Furthermore, the object of the invention is to provide an axial flux machine with the improved reduction of capacitive coupling.

[0010] This object is achieved by an electric machine with a shielding structure for reducing capacitive coupling in an electric machine, in particular a synchronous electric machine, wherein the shielding structure is located in the air gap of the electric machine and / or the shielding structure encompasses the winding heads of the stator. Furthermore, the object is achieved by an axial flux machine with a shielding structure according to the invention.

[0011] The invention relates to an electric machine with a shielding structure for reducing capacitive coupling in an electric machine, in particular a synchronous electric machine, wherein the electric machine has a rotor and a stator. The stator and the rotor are arranged spaced from one another by an air gap defined between an outer contour of the stator closest to the rotor and an outer contour of the rotor closest to the stator. The stator has winding overhangs, wherein the shielding structure is coupled to a housing of the electric machine or to the ground of the electric machine. According to the invention, the shielding structure lies in the air gap and / or the shielding structure comprises the winding overhangs of the stator.

[0012] In other words, by adding additional shielding to the electrical machine, the advantage is achieved that the capacitive coupling between the winding and rotor and thus the bearing voltage ratio (BVR) is reduced. For this purpose, an electrically conductive structure is used which, through its design, minimizes the formation of eddy currents in this shielding structure. The preferred direction of this structure is axial for a radial flux machine and radial for an axial flux machine. The shielding splits the capacitance between the winding overhang and shaft into two individual capacitances (winding overhang-shielding capacitance and shield-shaft capacitance). If the shielding is introduced without further changes to the geometries of the winding overhang and shaft, these new capacitances are each larger than the original capacitance. However, due to the grounding of the shielding, the capacitive couplings are reduced.

[0013] Advantageous embodiments are claimed in the subclaims and are explained in more detail below.

[0014] Advantageously, the shielding structure surrounds the stator winding heads in a V- or L-shape. In other words, the shielding structure surrounds the winding heads on two interconnected sides. This geometric arrangement has the advantage of more effective shielding of the winding heads.

[0015] In a preferred embodiment, the shielding structure is arranged in the air gap and covers the entire surface of the stator. This results in extensive shielding of the stator from the rotor, thus reducing the influence of capacitive coupling.

[0016] In a preferred embodiment, the shielding structure is arranged in slots of the stator.

[0017] The shielding structure is preferably designed in the form of a rail or comb. The comb has a grounding ring as a base body, from which a plurality of prongs protrude. The shielding structure particularly preferably forms a grid structure.

[0018] Advantageously, the tines have an axial section that transitions into a radial section after a bend. This creates an L-shaped structure, and the L-shaped structure surrounds the shielding structure of the winding heads.

[0019] Preferably, the tines have alternating long and short radial sections in the circumferential direction. The radial sections are either the same length as the axial sections, or twice as long or three times as long as an axial section. Alternatively, the radial sections can be several times longer than the axial sections.

[0020] The shielding structure is preferably flat or segmented. If the shielding structure is flat, it is predominantly cylindrical in the case of an RFM or shaped like a ring disk in the case of an AFM. However, if the shielding structure is segmented, only the grooves and, if applicable, the winding head areas can be covered.

[0021] In a preferred embodiment, the shielding structure is made of an electrically conductive but non-ferromagnetic material, particularly aluminum. This has little or no effect on the magnetic properties of the electrical machine. Alternatively, the shielding structure is made of an electrically conductive and ferromagnetic material, such as iron. This allows for both electrostatic and magnetic shielding. A shielding structure made of iron is preferably used in an RFM.

[0022] The shielding structure can be applied as a standalone element / component or as a coating, similar to a circuit board coating, to a cover / shield which is arranged in an air gap between the rotor and stator.

[0023] In other words, the electric machine has a seal between the space with the windings / winding overhangs and the rotor shaft / rotor or air gap. This seal also runs radially inside the winding overhangs in the axial direction to the yoke, where the seal to the stator housing is created. This seal is used as a carrier for the shielding, so no further component is required; instead, only a coating has to be applied (e.g., similar to the manufacture of printed circuit boards). The earth contact of the shielding to the housing is made in the area of ​​the mechanical fixation of the seal to the housing. This can be arranged, for example, as shown. Advantageously, the axial clamping force on the seal also acts directly on the earth contact. The AFM has a seal between the stator and the air gap so that the coolant can circulate in the winding slots without contaminating the air gap.This seal also extends radially within the winding overhangs in the axial direction to the yoke, where it seals against the stator housing. The shielding / shielding structure consists of comb-shaped conductors, whose prong-shaped conductors extend largely in the direction of the rotor shaft's rotational axis. This comb / prong shape serves to reduce and prevent eddy currents in the shielding.

[0024] Furthermore, the invention discloses an axial flux machine with a shielding structure according to the invention, wherein the shielding structure has the features described above.

[0025] Preferably, the shielding structure is arranged radially outward in the air gap of the axial flow machine and is provided with a part extending in the radial direction.

[0026] The invention is explained in more detail below with the aid of a drawing. It shows:

[0027] Fig. 1 is a sectional view of a first embodiment of a shielding structure according to the invention in an electrical machine,

[0028] Fig. 2 is a sectional view of a second embodiment of a shielding structure according to the invention in an electrical machine,

[0029] Fig. 3 is a sectional view of a third shielding structure according to the invention in an electrical machine.

[0030] The figures are merely schematic and serve only to clarify the invention. The same elements are designated by the same reference numerals.

[0031] While the figures are more focused on a linear structure, a flat structure is also useful and should be covered. Fig. 1 shows a sectional view of a first embodiment of a shielding structure 1 according to the invention in an electrical machine 2. The electrical machine 2, in particular an axial flux machine, has a stator 4 and a rotor 3 (not shown). In the illustrated embodiment, the axial flux machine has an I-arrangement, whereby the shielding structure described below can also be applied analogously to an H-arrangement of the axial flux machine.

[0032] The stator 4 comprises winding overhangs 6 arranged axially inwardly, wherein the stator 4 and the rotor 3 are arranged spaced from one another by an air gap 5 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. A seal 15 is arranged in the air gap and in an L-shape surrounding the winding overhangs 6 of the stator 4. The seal 15 further has a shielding structure 1, which in the illustrated embodiment is designed as a coating, similar to a printed circuit board coating. Alternatively, the shielding structure 1 can be designed as a separate component and arranged on or in the seal 15.

[0033] The shielding structure 1 is designed like a rail or comb 9, with the comb having a grounding ring 10 as its base body. A plurality of prongs 11 extend from the grounding ring 10. The prongs have an axial section 12, which, after a bend 13, transitions into a radial section 14. This results in the L-shaped shielding structure 1, which surrounds the winding heads 6 of the stator 4. The seal 15 and the grounding ring 10 of the shielding structure 1 are coupled to a housing 7, which acts as a ground, thus reducing capacitive coupling.

[0034] Fig. 2 shows a sectional view of a second embodiment of a shielding structure 1 according to the invention in an electrical machine 2. The arrangement of the shielding structure 1 corresponds to the arrangement in the first embodiment in Fig. 1. The difference remains that the radial section 14 of the shielding structure 1 extends into grooves 8 of the stator 4 and the seal 15, respectively. In this segmented representation of the shielding structure 1, some prongs 11 in the radial section 14 are several times longer, approximately three times longer, than those of the axial section 12.

[0035] Fig. 3 shows a sectional view of a third embodiment of a shielding structure 1 according to the invention in an electrical machine 2. The arrangement of the shielding structure 1 corresponds to the arrangement in the first and second embodiments in Fig. 1 and Fig. 2. The difference remains that the radial section 14 of the shielding structure 1 extends over the entire stator 4 or over the entire seal 15.

[0036] 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 similar features without establishing a priority.

[0037] List of reference symbols

[0038] 1 Shielding structure

[0039] 2 electric machine 3 rotor

[0040] 4 Stator

[0041] 5 Air gap

[0042] 6 winding heads

[0043] 7 Housing 8 Groove

[0044] 9 Comb

[0045] 10 Grounding ring

[0046] 11 prongs

[0047] 12 Axial section 13 Bend

[0048] 14 Radial section

[0049] 15 Sealing

Claims

Claims 1. An electric machine having a shielding structure (1) for reducing capacitive coupling in an electric machine (2), in particular a synchronous electric machine, the electric machine having a rotor (3) and a stator (4), the stator (4) and the rotor (3) being arranged at a distance from one another by an air gap (5) 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), and the stator (4) having windings and winding heads (6), the shielding structure (1) being coupled to a housing (7) of the electric machine (2) or to the ground of the electric machine (2), characterized in that the shielding structure (1) lies in the air gap (5) and / or the shielding structure (1) comprises the winding heads (6) of the stator (4).

2. Electric machine with a shielding structure (1) according to claim 1, characterized in that the shielding structure (1) surrounds the windings and winding heads (6) of the stator (4) in a V- or L-shape.

3. Electric machine with a shielding structure (1) according to claim 1 or 2, characterized in that the shielding structure (1) arranged in the air gap (5) covers the entire stator (4) in a planar manner.

4. Electric machine with a shielding structure (1) according to one of claims 1 to 3, characterized in that the shielding structure (1) is arranged in grooves (8) of the stator (4).

5. Electric machine with a shielding structure (1) according to one of claims 1 to 4, characterized in that the shielding structure (1) is designed in the manner of a rail or comb (9), wherein the comb (9) has an earthing ring (10) as a base body, from which a plurality of prongs (11) protrude.

6. Electric machine with a shielding structure (1) according to one of claims 1 to 5, characterized in that the shielding structure (1) forms a grid structure.

7. Electric machine with a shielding structure (1) according to one of claims 1 to 6, characterized in that the tines (11) have an axial section (12) which, after a bend (13), merges into a radial section (14).

8. Electric machine with a shielding structure (1) according to one of claims 1 to 7, characterized in that the tines (11) have alternating long and short radial sections (14) in the circumferential direction and the radial sections (14) are of the same length as the axial sections (12) or twice as long or 3 times as long as an axial section (12).

9. Electric machine with a shielding structure (1) according to one of claims 1 to 8, characterized in that the shielding structure (1) is flat or segmented.

10. Electric machine with a shielding structure (1) according to one of claims 1 to 9, characterized in that the shielding structure (1) is formed from an electrically conductive but non-ferromagnetic material or from an electrically conductive and ferromagnetic material. 11 .Axial flux machine with a shielding structure (1) according to one of the preceding claims.

12. Axial flux machine according to claim 11, characterized in that the shielding structure (1) is arranged radially outward in the air gap and is provided with a part extending in the radial direction.

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