Electric machine having shielding structure for reducing capacitive coupling in electric machine and axial flux electric machine having such 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 a synchronous machine, the electric machine having a rotor (3) and a stator (4), the stator (4) and the rotor (3) being spaced apart from one another by an air gap (5), the invention relates to an electric machine (2) comprising a stator (4) having an air gap (5) defined between an outer contour of the stator (4) positioned closest to the rotor (3) and an outer contour of the rotor (3) positioned closest to the stator (4), and the stator (4) having a winding head (6), in which the shielding structure (1) is coupled to a housing (7) of the electric machine (2) or to a ground of the electric machine (2), characterized in that the shielding structure (1) is located in the air gap (5) and / or the shielding structure (1) encloses the winding head (6) of the stator (4).

Description

Technical Field

[0001] This invention relates to a motor with a shielding structure for reducing capacitive coupling in the motor, particularly a synchronous motor, having a rotor and a stator spaced apart by an air gap defined between the outer contour of the stator positioned closest to the rotor and the outer contour of the rotor positioned closest to the stator, and the stator having winding heads. The shielding structure is connected to the motor housing or the motor grounding terminal. The invention also relates to an axial flux motor having a shielding structure according to the invention. Background Technology

[0002] The development of electric drives increasingly focuses on efficiency, with the greatest potential lying in improvements to inverter technology. Meanwhile, improvements in power module technology are linked to key technical challenges. One such challenge is the increase in parasitic currents in the system, which not only causes electromagnetic compatibility (EMC) issues but also induces various types of bearing currents, potentially leading to shortened bearing life and ultimately premature system failure.

[0003] In inverter-fed electric drive systems, three types of bearing currents can be distinguished: discharge current (EDM), circulating current, and rotor-to-ground current. The cause of all these currents is the inverter, which does not provide a continuous voltage level to drive the motor. Switches in the inverter's power module toggle between battery voltage levels (+ and -) to generate a sinusoidal current. This switching method generates a common-mode voltage that is responsible for the bearing currents. This shaft voltage creates an electric field between the rotor and the stator or ground. Due to these capacitive couplings between the stator windings and the rotor shaft, a potential is generated at the motor shaft. These potentials cause spark discharges in the bearings and result in leakage currents through the bearings, which can damage them.

[0004] Measures to prevent spark discharge and bearing current are known, such as using special contact brushes to ground the rotor shaft, using ceramic balls to insulate the bearing, or insulating the inner or outer ring of the bearing.

[0005] Another measure, in the form of an integrated electrostatic shield, is known from DE 10 2017 208 634 A1. In radial flux motors (RFMs), a defined capacitance between the windings and the rotor shaft is formed by copper conductors in the winding slots. Therefore, DE 10 2017 208 634 A1 describes a slot closure in the form of a covered slide, wherein an integrated electrostatic shield is provided between the copper conductors in the winding slots and the rotor to reduce shaft voltage.

[0006] In axial flux motors (AFM), particularly in configurations with rotors having plastic supports that electrically insulate the magnets from the rotor shaft, capacitance is distributed in a significantly different manner compared to radial flux motors. The defined capacitance between the windings and the rotor shaft is determined by the radially inner winding heads.

[0007] The plastic support that electrically insulates the magnets from the rotor shaft forms an additional capacitance with the rotor capacitance of the windings in series. Because the rotor-shaft capacitance is typically very small due to its geometry, the effective capacitance between the windings and the rotor is also very small due to the series connection. Therefore, the winding conductors in the winding slots have only a very small effect on the shaft voltage. Due to the close proximity of the radially inner winding heads to the rotor shaft, these formed capacitances are significantly larger than the aforementioned capacitance between the conductors in the winding slots and the rotor shaft. Therefore, this is decisive for the shaft voltage and must be considered in aspects such as bearing current. Summary of the Invention

[0008] Therefore, an object of the present invention is to provide an improved reduction in capacitive coupling in order to overcome the disadvantages of the prior art. Another object of the present invention is to provide an axial flux motor with improved reduced capacitive coupling.

[0009] This objective is achieved by a motor with a shielding structure designed to reduce capacitive coupling in the motor, particularly a synchronous motor, wherein the shielding structure is located in the air gap of the motor and / or encloses the winding heads of the stator. Furthermore, this objective is achieved by an axial flux motor with a shielding structure according to the invention.

[0010] This invention relates to a motor with a shielding structure for reducing capacitive coupling in the motor, particularly a synchronous motor, having a rotor and a stator. The stator and rotor are arranged to be spaced apart from each other by an air gap defined between the outer contour of the stator positioned closest to the rotor and the outer contour of the rotor positioned closest to the stator. The stator has winding heads, and the shielding structure is connected to the motor housing or the motor grounding terminal. According to the invention, the shielding structure is located in the air gap and / or the shielding structure encloses the winding heads of the stator.

[0011] In other words, adding additional shielding to the motor achieves the following advantages: reduced capacitive coupling between the windings and the rotor, and therefore a reduced transmission ratio (BVR, bearing voltage ratio). For this purpose, an electrically conductive structure is used, which, due to its design, minimizes the formation of eddy currents in the shielding structure. For radial flux motors, the preferred orientation of this structure is axial, and for axial flux motors, the preferred orientation is radial. The shielding divides the capacitance between the winding head and the shaft into two separate capacitances (winding head-shielding capacitance and shielding-shaft capacitance). If the shielding is introduced without further altering the geometry of the winding head and shaft, these new capacitances are each larger than the original capacitances. However, due to the grounding of the shielding, capacitive coupling is reduced.

[0012] Advantageous embodiments are claimed in the dependent claims and are described in more detail below.

[0013] Advantageously, the shielding structure surrounds the stator winding head in a V-shape or L-shape. In other words, the shielding structure surrounds the winding head on two interconnected sides. This geometric arrangement has the advantage of more effective shielding of the winding head.

[0014] 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 and rotor, and thus reduces the effects of capacitive coupling.

[0015] In a preferred embodiment, the shielding structure is arranged in a slot in the stator.

[0016] The shielding structure is preferably designed in the form of a track or comb. The comb has a grounding ring as its main body, from which multiple forks protrude. Particularly preferably, the shielding structure forms a mesh structure.

[0017] Advantageously, the fork-shaped part has an axial portion that transitions to a radial portion after the bend. This results in an L-shaped structure that surrounds the shielding structure of the assembly head.

[0018] Preferably, the fork has alternating long and short radial portions in the circumferential direction. The length of the radial portion is the same as the length of the axial portion, or two or three times the length of the axial portion. Alternatively, the radial portion can be many times longer than the axial portion.

[0019] Preferably, the shielding structure is flat or segmented. If the shielding structure is flat, it is primarily cylindrical in the case of RFM, or shaped like an annular disk in the case of AFM. However, if the shielding structure is segmented, only the slots and optional winding heads can be covered.

[0020] In a preferred embodiment, the shielding structure is formed of a conductive but non-ferromagnetic material, particularly aluminum. This means that the magnetism in the motor is unaffected or only slightly affected. Alternatively, the shielding structure is formed of a conductive and ferromagnetic material, such as iron. This allows for both electrostatic and magnetic shielding. Ferrous shielding structures are preferably used in RFM.

[0021] The shielding structure can be used as a separate component or as a coating similar to that of a circuit board, applied to a cover / shielding element arranged in the air gap between the rotor and the stator.

[0022] In other words, the motor has a seal between the space with the windings / winding heads and the rotor shaft / rotor or air gap. This seal also extends radially in the axial direction inside the winding heads to the yoke, where a seal is made relative to the stator housing. This seal serves as a support for the shield, eliminating the need for additional components and requiring only the application of a coating (e.g., similar to circuit board production). The ground contact of the shield relative to the housing occurs in the area where the seal is mechanically fixed to the housing. For example, this can be arranged as shown. Advantageously, the axial clamping force on the seal also acts on the ground contact. The AFM has a seal between the stator and the air gap, allowing coolant to circulate in the winding slots without contaminating the air gap. This seal also extends radially in the axial direction inside the winding heads to the yoke, where a seal is made relative to the stator housing. The shield / shielding structure consists of comb-shaped conductors, whose forked conductors extend primarily along the direction of the rotor shaft's rotation axis. This comb / forked shape is used to reduce and avoid eddy currents in the shield.

[0023] Furthermore, the present invention discloses an axial flux motor having a shielding structure according to the present invention, wherein the shielding structure has the above-mentioned features.

[0024] Preferably, the shielding structure is arranged radially outward in the air gap of the axial flux motor, and has a portion extending in the radial direction. Attached Figure Description

[0025] The invention will now be described in more detail with the aid of the accompanying drawings.

[0026] In the attached diagram:

[0027] Figure 1 A cross-sectional view of a first embodiment of the shielding structure according to the present invention in an electric motor is shown.

[0028] Figure 2 A cross-sectional view of a second embodiment of the shielding structure according to the present invention in an electric motor is shown.

[0029] Figure 3A cross-sectional view of the third shielding structure according to the present invention in the motor is shown. Detailed Implementation

[0030] The accompanying drawings are purely illustrative and intended only to understand the invention. The same elements are designated with the same reference numerals.

[0031] While the attached diagram is more suitable for linear structures, mesh structures are also useful and intended to be covered.

[0032] Figure 1 A cross-sectional view of a first embodiment of the shielding structure 1 according to the invention in an electric motor 2 is shown. The electric motor 2, particularly an axial flux motor, has a stator 4 and a rotor 3 (not shown). In the illustrated embodiment, the axial flux motor is arranged in an I-shape, wherein the shielding structure described below can also be similarly applied to an H-shape arrangement of the axial flux motor.

[0033] The stator 4 includes an axially inwardly arranged winding head 6, wherein the stator 4 and the rotor 3 are arranged to be spaced apart from each other by an air gap 5 defined between the outer contour of the stator 4 positioned closest to the rotor 3 and the outer contour of the rotor 3 positioned closest to the stator 4. A seal 15 is arranged in the air gap and surrounds the winding head 6 of the stator 4 in an L-shape. The seal 15 also includes a shielding structure 1, which in the illustrated embodiment is implemented as a coating, similar to a circuit board coating. Alternatively, the shielding structure 1 may be designed as a separate component and arranged on or within the seal 15.

[0034] The shielding structure 1 is designed as a type of track-like or comb-like structure 9, wherein the comb-like structure has a grounding ring 10 as its main body. Multiple forks 11 extend from the grounding ring 10. The forks have axial portions 12 that transition to radial portions 14 after a bend 13. This results in an L-shaped shielding structure 1 that surrounds the winding head 6 of the stator 4. A seal 15 is connected to the grounding ring 10 of the shielding structure 1 to a housing 7 serving as a grounding terminal, thereby reducing capacitive coupling.

[0035] Figure 2 A cross-sectional view of a second embodiment of the shielding structure 1 according to the present invention in the motor 2 is shown. The arrangement of the shielding structure 1 is similar to... Figure 1 The arrangement corresponds to that in the first embodiment. The difference is that the radial portion 14 of the shielding structure 1 extends in the groove 8 of the seal 15 or the stator 4. In this section representation of the shielding structure 1, some of the forks 11 in the radial portion 14 are several times longer, approximately three times longer, than some of the forks in the axial portion 12.

[0036] Figure 3A cross-sectional view of a third embodiment of the shielding structure 1 according to the present invention in the motor 2 is shown. The arrangement of the shielding structure 1 is similar to... Figure 1 First implementation method and Figure 2 The arrangement corresponds to that in the second embodiment. The difference is that the radial portion 14 of the shielding structure 1 extends over the entire stator 4 or extensively over the entire seal 15.

[0037] This invention is not limited to the embodiments shown in the accompanying drawings. Therefore, the above description should not be considered limiting but rather illustrative. The appended claims should be understood to indicate the presence of the stated features in at least one embodiment of the invention. This does not exclude the presence of other features. Where the claims and the above description define "first" and "second" features, this designation is used to distinguish between two features of the same type, without specifying any order of priority.

[0038] List of reference numerals

[0039] 1. Shielding structure

[0040] 2 motors

[0041] 3 rotors

[0042] 4. Stator

[0043] 5. Air gap

[0044] 6 Winding head

[0045] 7. Casing

[0046] 8 slots

[0047] 9. Comb-like structures

[0048] 10 Grounding ring

[0049] 11 Forked objects

[0050] 12 Axial section

[0051] 13. Bend

[0052] 14 Radial portion

[0053] 15. Seals.

Claims

1. A motor having a shielding structure (1) for reducing capacitive coupling in a motor (2), particularly a synchronous motor, the motor having a rotor (3) and a stator (4) spaced apart from each other by an air gap (5) defined between the outer contour of the stator (4) positioned closest to the rotor (3) and the outer contour of the rotor (3) positioned closest to the stator (4), and the stator (4) having windings and winding heads (6), the shielding structure (1) being connected to a housing (7) of the motor (2) or a ground terminal of the motor (2), characterized in that, The shielding structure (1) is located in the air gap (5) and / or the shielding structure (1) encloses the winding head (6) of the stator (4).

2. The motor with 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-shape or L-shape.

3. The motor with shielding structure (1) according to claim 1 or 2, characterized in that, The shielding structure (1) arranged in the air gap (5) extensively covers the entire stator (4).

4. The motor with shielding structure (1) according to any one of claims 1 to 3, characterized in that, The shielding structure (1) is arranged in the slot (8) in the stator (4).

5. The motor with shielding structure (1) according to any one of claims 1 to 4, characterized in that, The shielding structure (1) is designed in the form of a track or a comb (9), the comb (9) having a grounding ring (10) as its main body, from which a plurality of forks (11) protrude.

6. The motor with shielding structure (1) according to any one of claims 1 to 5, characterized in that, The shielding structure (1) forms a mesh structure.

7. The motor with shielding structure (1) according to any one of claims 1 to 6, characterized in that, The fork (11) has an axial portion (12) that transitions to a radial portion (14) after a bend (13).

8. The motor having a shielding structure (1) according to any one of claims 1 to 7, characterized in that, The fork (11) has alternating long radial portions and short radial portions (14) in the circumferential direction, and the length of the radial portion (14) is the same as or two or three times the length of the axial portion (12).

9. The motor having a shielding structure (1) according to any one of claims 1 to 8, characterized in that, The shielding structure (1) is flat or segmented.

10. The motor having a shielding structure (1) according to any one of claims 1 to 9, characterized in that, The shielding structure (1) is formed of a conductive but non-ferromagnetic material or a conductive and ferromagnetic material.

11. An axial flux motor having a shielding structure (1) according to any one of the preceding claims.

12. The axial flux motor according to claim 11, characterized in that, The shielding structure (1) is arranged radially outward in the air gap and has a portion extending radially.

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