ACTIVE MAGNETIC BEARING WITH REDUCED LOSS POWER

Description

[0001] The invention relates to an active magnetic bearing and a method for its manufacture. Background of the invention

[0002] An active magnetic bearing (AMB) according to the state of the art is used in connection with Fig. 1 The active magnetic bearing 100 is used to levitate a rotating rotor 1, allowing the rotor 1 to rotate about an axis of rotation 10 without mechanical contact with a bearing device. This results in low-friction rotation of the rotor 1 compared to rotors supported by, for example, plain or ball bearings. At the same time, controlled force application minimizes vibrations, enabling operation even at critical speeds.

[0003] The active magnetic bearing comprises a stator 2 and a section mounted on the rotor 1, which typically includes magnetically conductive laminations and is therefore also referred to as the rotor lamination stack 1a. The rotor lamination stack 1a is located on the rotor 1 opposite the stator 2, i.e., in a rotor receptacle 8. The rotor lamination stack can be considered part of the rotor 1.

[0004] The stator 2 comprises a pole tooth 4 designed to conduct a magnetic flux density. A magnetic flux associated with the magnetic flux density results from the integration of a normal component of the magnetic flux density over a surface through which the magnetic flux density passes. The magnetic flux is guided by the pole tooth 4 in a substantially radial direction 11, where the radial direction 11 is defined perpendicular to the axis of rotation 10. During operation of the AMB, the magnetic flux can enter the rotor lamination stack 1a from the pole tooth 4 through a gap 3. In cross-section, the pole tooth 4 has a substantially trapezoidal shape, with the side facing the rotor 1, here referred to as the pole tooth surface 17, following the rotor contour and being spaced from the rotor 1 and the rotor lamination stack 1a by the gap 3.

[0005] A pole gap 5 is arranged in a circumferential direction 12 adjacent to the pole tooth 4. The pole gap 5 does not serve to conduct the magnetic flux in the radial direction 11. Generally, the pole gap 5 comprises a cavity into which a winding of a coil is inserted. The magnetic flux in the radial direction 11 is smaller in magnitude in the region of the pole gap 5 than in the region of the pole tooth 4 and can even disappear completely in the pole gap 5.

[0006] As the rotor 1 rotates, a rotor point 21 on and / or near the surface of the rotor lamination stack 1a sweeps over an area of ​​high radial magnetic flux density in the region of the pole tooth 4 and an area of ​​lower (than at the pole tooth) and / or no radial magnetic flux density in the region of the pole gap. Due to the change in radial magnetic flux density that the rotor point 21 experiences on the rotor lamination stack when transitioning from pole tooth 4 to pole gap 5 or from pole gap 5 to pole tooth 4, a current called an eddy current is generated in the rotor point 21. The flow of this eddy current leads to power loss in the rotor lamination stack (1a) or more generally in the rotor (1), and thus to its heating, which is undesirable and generally requires cooling, possibly active cooling.

[0007] The amount of power loss in the rotor lamination stack 1a or more generally in the rotor is a function of the time change of the magnetic flux or more precisely the magnetic flux density, for example the radial magnetic flux density, which the rotor point 21 experiences.

[0008] US Patent 5,142,175 A deals with the reduction of eddy currents. The document describes a system for carrying a rotor without contact with a stator, comprising a magnetic bearing device mounted on the stator, a controllable magnet attached to the stator, a non-controllable magnet pole attached to the stator, a pre-magnetizing magnet pole positioned between the controllable magnet and the non-controllable magnet pole, and a rotor magnet pole attached to the rotor to allow the magnetic path of a pre-magnetizing flux to lie in a plane that includes the longitudinal axis of the stator. The non-controllable magnet pole and the rotor magnet pole may have opposing teeth.

[0009] EP 2 148 103 A1 describes a magnetic radial bearing for the contactless support of a rotor shaft. The publication deals with the particularly simple design of a magnetic bearing system. The magnetic radial bearing has a rotating field machine stator with a number n of stator slots distributed circumferentially and an equal number n of stator teeth between them. The stator slots are wound with a multiphase stator winding to generate a rotating magnetic field. An axially extending, strip- or plate-shaped permanent magnet is arranged at each radial end of the stator teeth, the permanent magnets having an alternating radial magnetization direction in the circumferential direction.

[0010] DE 2 338 307 A1 describes an electromagnetic drive for rotating bodies consisting of a stationary part having at least two magnetic coils and a rotating part with magnetizable material, wherein, in addition to the control of the magnetic coils for driving the rotating part, these or parts of their windings are also controlled by a control device which is linked to a measuring system that detects the radial position of the rotating body.

[0011] US Patent 6,885,127 B1 describes a stator for an automotive generator. The stator includes a stator core in which a plurality of slots are formed around its inner circumference, stator coils fitted into the slots, and a rotor provided within the stator to allow it to rotate, including a rotor coil for carrying a current to generate a magnetic flux, and a pole core to receive the rotor coil and form a plurality of claw-shaped magnetic poles in accordance with the magnetic flux.Two slots are provided for each set of stator coils, each phase and each magnetic pole having a total number of slots of seventy-two or more, and the stator core being constructed such that a plurality of sheet-like magnetic elements with a plurality of teeth structuring the slots on one side of a yoke are laminated, the stator coils being arranged in the slots, and the stator core being rounded such that the stator coils become its inside and its two end faces are contacted to join the stator core in a ring shape.

[0012] On the stationary side of a radial bearing constructed from multiple magnetic poles, as described in US Patent 6,194,800 B1, the magnetic poles are shaped such that the magnetic flux density distribution between the inner surfaces of these magnetic poles and a rotor located on the rotating side is inclined from the end section of the magnetic pole to the middle section. This arrangement reduces the rate of change of the magnetic flux density during the movement of the rotor from one magnetic pole to the adjacent magnetic pole, thereby reducing eddy current loss and heat generation.

[0013] EP 1 411 255 A1 describes stator cores for a homopolar magnetic bearing, wherein toothed ends of the stator cores form N-poles and S-poles adjacent to each other in the axial direction around a rotor. A manufacturing method is also described. The stator core is provided with projections of adjacent N- and S-poles extending around the circumference so that they are in contact with or in close proximity to each other, and consists of U-shaped laminated steel sheets interleaved with an insulating material. The center side is open from the centerline side. Furthermore, the core comprises a first yoke, a second yoke, and a shaft unit, which is a magnetic body placed and fixed between the yokes. At least the shaft unit consists of a magnetic material powder solidified in resin.

[0014] In US Patent 2017 / 0288476 A1, an active part for an electric machine can be configured as a stator or rotor and includes at least two slots for arranging an electrical coil winding. A crossbar is arranged between the two slots, made of a material that conducts a magnetic flux through the electrical coil surrounding the crossbar. The material exhibits magnetic anisotropy in at least one region, with a slight magnetization axis oriented parallel to, or at least at an angle of less than 25° to, a coil axis, and a hard magnetization axis. The crossbar is configured to form a slotted wall for each of the slots, containing the material. The crossbar includes a core made of an isotropic soft magnetic material.

[0015] DE 198 43 522 A1 describes a device with a printed circuit board located in the end windings of the stator. This board is equipped with all the components necessary for monitoring the air gap between the stator and rotor. These components include Hall sensors, eddy current sensors, temperature sensors with all the necessary components for processing the signals, and the power electronics for controlling the windings.

[0016] In US Patent 7,579,723 B2, a power magnetic core has a start section and an end section. Magnetic field lines form within the powder magnetic core from the start to the end section. The powder magnetic core comprises a first section, located on the shortest magnetic path of the field lines connecting the start and end sections, and exhibiting a permeability of µa, and a second section, located off the shortest magnetic path of the field lines, exhibiting a permeability µb greater than µa. This design achieves the desired magnetic properties and sufficiently reduces iron loss.

[0017] In US Patent 2021 / 0013771 A1, an electric motor comprises a rotor rotatably mounted about an axially oriented axis of rotation and a stator comprising stator teeth that are T-shaped at the root end to form pole tabs and extend circumferentially. The pole tabs may form a contact shoulder. A stator slot for receiving coils of a stator winding is formed between adjacent stator teeth, and a slot opening is formed between facing pole tabs. A reinforcing element may be inserted into a slot opening. The reinforcing elements are held against the facing pole tabs of adjacent stator teeth by the contact shoulders. The reinforcing element has a contour that engages in a bearing area to reduce the contact area with the bearing shoulders.

[0018] WO 2014 / 048 464 A1 deals with increasing the magnetic flux density in an active component, such as one found in a magnetic bearing, in a cost-effective manner. The publication describes an active component of an electric machine with teeth, each having a tooth root and a tooth height, open or closed slots arranged between the teeth, and windings inserted in the slots, each enclosing at least one of the teeth. The active component has a thickness greater than the tooth height, extending from the outer surface of the respective tooth roots and along the teeth. Furthermore, such an electric machine, a radial magnetic bearing with such an active component, and a method for manufacturing such a radial magnetic bearing are described.In order to provide an active part that has comparatively good magnetic properties and is inexpensive to manufacture, it is proposed that the active part, starting from the respective tooth root up to a limiting depth which is at most equal to the tooth height, comprises a first material with a first magnetic permeability and from the limiting depth comprises a second material with a second magnetic permeability, wherein the first magnetic permeability is greater than the second magnetic permeability.

[0019] The object of the invention is to reduce power loss in the rotor lamination stack, or more generally in the rotor or a section of the rotor of an active magnetic bearing, and thus to provide an improved active magnetic bearing and a stator for such an improved active magnetic bearing, as well as a method for its manufacture. This allows for a reduction in heating and therefore the necessary cooling, making the machine more cost-effective in design and operation, less energy-intensive, and thus more environmentally friendly.

[0020] The invention is solved according to the invention by a stator with the features of claim 1, an active magnetic bearing with the features of claim 7, and a method with the features of claim 8. Advantageous embodiments are set forth in the dependent claims. Inventive idea

[0021] Power loss can be reduced by decreasing the rate of change of magnetic flux or magnetic flux density, particularly the radial component of the magnetic flux density experienced at a point on the rotor (rotor point) during rotation. This is achieved by ensuring that the decrease and / or increase in radial magnetic flux density as it passes over the pole tooth and / or pole gap is as smooth as possible. Therefore, a gradual increase and / or decrease in the radial component of the magnetic flux density is desirable towards the circumferential edge(s) of the pole tooth.

[0022] The terms magnetic flux density in the radial direction, radial component of the magnetic flux density, radial component of the magnetic flux density and radial magnetic flux density are used synonymously.

[0023] Those skilled in the art are aware that the magnetic flux density depends on the magnetic permeability of the material at the point where the magnetic flux density is observed or measured. Since a fixed point on the rotor is always used for considering the resulting eddy currents, the material properties at the point of observation do not change. For the qualitative description, the material properties at the rotor point are irrelevant, apart from the fact that magnetic permeability must be present. In the stator, however, the material properties are important.

[0024] In particular, a stator of an active magnetic bearing with an axial receptacle for a rotor spaced from the stator by a gap, which is designed to guide a magnetic flux density and to rotate about an axis of rotation arranged in the axial direction perpendicular to a cross-sectional area of ​​the axial receptacle, and with a pole tooth comprising a pole tooth surface forming a circumferential section of the axial receptacle, and two pole tooth side surfaces which delimit the pole tooth on both sides against an adjacent pole gap in a circumferential direction oriented perpendicular to the axial direction, wherein the pole tooth is designed to guide the magnetic flux density such that at a center of the pole tooth surface the outgoing or incoming magnetic flux density has a maximum value in a radial direction oriented perpendicular to the axial direction and perpendicular to the circumferential direction,and wherein the material of the pole tooth exhibits an inhomogeneity of permeability with respect to the circumferential direction, preferably at least at or adjacent to the pole tooth surface.

[0025] The pole tooth comprises a magnetically conductive material. For example, this can be a magnetically conductive sheet or soft magnetic composite (SMC).

[0026] The pole tooth material does not include a permanent magnet.

[0027] Furthermore, an active magnetic bearing is created, comprising a stator and rotor as described above, which is arranged spaced apart by the gap in the axial receptacle of the stator and is designed to guide the magnetic flux density and to rotate about the axis of rotation arranged perpendicular to the cross-sectional area of ​​the axial receptacle in the axial direction.

[0028] The pole tooth or pole teeth of the stator are separated from the rotor only by the gap in which a vacuum or a fluid, for example in a gaseous state of matter, in particular air, is arranged.

[0029] This results in a stator with a pole tooth configured to conduct a radial magnetic flux density, decreasing in magnitude relative to the center or central region of the pole tooth surface, towards one or both pole tooth surfaces on a side facing the rotor, relative to its circumferential extent. This means that the pole tooth is designed such that the radial component of the magnetic flux density at the pole tooth surface varies depending on its position in the circumferential direction; that is, its magnitude decreases less abruptly towards one or both pole tooth surfaces than in a prior art pole tooth where the pole tooth surfaces adjacent to the pole tooth surface facing the rotor are essentially flat and planar.The maximum of the radial component of the magnetic flux density does not necessarily lie in the center of the pole tooth, i.e., in the center of the pole tooth surface. However, the maximum does occur in the center of the pole tooth surface, that is, not at its edge, but in a region encompassing the center.

[0030] This further means that near the position of the pole tooth side surface in the circumferential direction, the magnitude of a derivative of the continuous course of the radial component of the magnetic flux density at the surface of the rotor with respect to a path length in the circumferential direction is always smaller than the derivative of the radial component of the magnetic flux density at the surface of the rotor with respect to a path length in the circumferential direction in the case of a substantially planar pole tooth side surface combined with a homogeneous permeability of the material in the pole tooth in the circumferential direction and / or the radial direction.

[0031] A method according to the invention for forming a stator of an active magnetic bearing or an active magnetic bearing comprises the following method steps: a) Providing a model that models at least the pole tooth with its surface and side faces, at least sections of the adjacent pole gaps, at least a section of the rotor separated by the gap, and a generation of the magnetic flux density in the pole tooth; b) Calculating the magnetic flux density at the rotor surface in the radial direction using the model as a function of its position in the circumferential direction; c) Calculating an evaluation function that assesses a measure of losses occurring in the rotor as a function of changes in the magnitude of the magnetic flux density in the radial direction at the rotor surface along a path length in the circumferential direction; d) Varying a permeability of the pole tooth material in the model; e) Iteratively performing steps b) to d) to determine an extremum of the evaluation function.g) Outputting information describing the pole tooth, for example its shape, according to the model, which corresponds to the determined extreme value of the evaluation function, and h) forming a stator or an active magnetic bearing with a pole tooth based on the output information, which corresponds to the pole tooth according to the model, for example with respect to its shape.

[0032] In order to vary the permeability in the pole tooth, the invention provides that the position and / or shape and / or extent and / or the filling material of one or more recesses in the pole tooth are varied.

[0033] The extreme value can, for example, be a minimum.

[0034] This allows for a reduction in the required cooling or even the complete elimination of active cooling. This leads to a further simplification of the active magnetic bearing's design.

[0035] The reduction in eddy currents can also be used to employ thicker laminations in the rotor's laminated core. This increases the rotor's mechanical stability. Furthermore, thicker laminations are easier to manufacture and handle.

[0036] According to the invention, the variation in permeability is configured such that one or more recesses are arranged in the pole tooth, which comprises a material, for example, iron, electrical steel, SMC, and / or a ferrite. The one or more recesses are each configured as cavities enclosed by the pole tooth material, at least in planes oriented perpendicular to the axial direction, and spaced apart from the pole tooth surface and optionally from the pole tooth side surface. Another material, for example, air or a solid material, which differs from the surrounding pole tooth material at least with respect to its magnetic properties, for example, its permeability, is arranged in the one or more recesses.

[0037] In one embodiment, in addition to varying the permeability of the pole tooth material, one or both pole tooth side surfaces adjacent to the pole tooth surface facing the rotor have a projection that tapers or spans the pole gap.

[0038] A further development of the procedure therefore provides in process step d) an additional variation of a geometric shape of the pole tooth, in particular of the pole tooth side surface adjacent to the pole tooth surface.

[0039] A projection protrudes from a flat and planar pole tooth surface that extends essentially radially into the stator. The formation of this projection on the pole tooth surface adjacent to the pole tooth surface generally increases the surface area of ​​this pole tooth surface. This is accompanied by a change in the radial component of the magnetic flux density adjacent to the pole gap, or above the pole gap if the projection spans or partially spans the pole gap. However, since the surface area is increased by forming a projection on one pole tooth surface or by forming a projection on each of the two pole tooth surfaces, the magnetic flux density is not reduced uniformly across the entire pole tooth surface. The distribution of magnetic field lines, particularly the radial component of the magnetic flux density, is affected by the formation of these projections on the pole tooth surfaces adjacent to the pole gap.The magnetic flux is more strongly affected at the pole gaps than at the center of the pole tooth surface. This leads to a decrease in the radial component of the magnetic flux density towards the edge(s) of the pole tooth surface in the circumferential direction. However, the total radial flux does not decrease significantly.

[0040] Preferably, the model is provided as a finite element model. Such a model is well-suited for modeling different geometric shapes as well as locally varying material properties.

[0041] Other embodiments can utilize parameterized functions and models to describe and model the pole tooth and / or the stator or the other elements of the active magnetic bearing. The shape of the pole tooth in the cross-sectional plane perpendicular to the rotor's axis of rotation can be described via parameterized functions, allowing the shape to be adjusted and varied by changing the parameters.

[0042] The projection preferably consists of a highly magnetically conductive material, wherein the highly magnetically conductive material has a high relative permeability µr, preferably greater than 500, and even more preferably greater than 1000. The permeability µ = µr · µ₀ is given as the product of the magnetic constant µ₀ and the relative permeability µr. The magnetic constant µ₀ is itself the reciprocal of the product of the electric constant ε₀ and the square of the speed of light c₂. This ensures that the magnetic flux travels radially through the projection. The projection can be formed, for example, using magnetically conductive sheet metal. Alternatively or additionally, soft magnetic composites (SMC) can also be used.In particular, printable magnetically conductive materials can also be used to produce the projection and / or the pole tooth using a 3D printing process.

[0043] It is conceivable that the projection of one of the pole tooth faces differs from a projection of the other pole tooth face and / or a projection of a pole tooth face of another pole tooth with respect to a geometric dimension and / or the inhomogeneity of permeability. This can be advantageous, for example, if several pole teeth are arranged in an active magnetic bearing and these have different geometric dimensions and / or are intended to conduct different magnetic flux densities.

[0044] However, the material thickness of the projection is small in the radial direction compared to the rest of the pole tooth. Therefore, in some embodiments, a support element is arranged on the projection in the pole gap to absorb forces acting on the projection.

[0045] It is particularly preferred that at least the support element comprises, or optionally is formed from, a material that has a lower permeability than the material of the pole tooth in the area of ​​the projection. This ensures that the magnetic field lines in the pole tooth and its immediate surroundings are only minimally or not at all affected by the support element. Therefore, its shape and other design can be freely chosen to optimally fulfill the mechanical requirements of force absorption.

[0046] In preferred embodiments, the support element is designed to fit snugly against the projection. This ensures particularly good force transmission into the at least one support element.

[0047] In addition to the shape of the pole tooth, a support element is also included in the model in some embodiments of the method and adapted via a variation.

[0048] Optimal conduction of the magnetic flux density between the pole tooth and the projection can be achieved in embodiments where the projection(s) are formed integrally with the rest of the pole tooth. In these embodiments, the mechanical contact between the pole tooth and the projection can result in greater mechanical stability of the projection, i.e., greater resistance to mechanical deformation in the event of force application, than in a multi-part embodiment.

[0049] In order to achieve high mechanical stability and to realize an optimal reduction of the magnetic flux density, in some embodiments the projection is provided that it spans the pole gap to such an extent that the projection touches a further projection of a further pole tooth side surface of a further adjacent pole tooth or is formed integrally with this further projection.

[0050] A multi-part embodiment of the pole tooth and projection can be advantageous during the assembly of the magnetic bearing stator. For example, it may be necessary to have initial access to the pole gap during a manufacturing step, and the projection could obstruct such access. In such a case, mounting the projection after the manufacturing step would be helpful. It is also conceivable that the projection is designed in multiple parts.

[0051] The support element can also be used to absorb or dissipate thermal loads. Some embodiments provide that the support element and the projection whose forces it absorbs, and / or the support element and the pole tooth, are thermally coupled.

[0052] Alternatively or additionally to modifying the geometric design of the pole tooth on one or both of its side faces compared to the essentially trapezoidal geometry of the pole tooth known from the prior art, the material of the pole tooth can also exhibit a variation in permeability on the pole tooth surface, for example, along the circumferential direction. For instance, the permeability can decrease from a section of the pole tooth surface located at its center, with a permeability given in this section, towards one or both pole tooth surfaces. This also ensures that a change in the radial component of the magnetic flux density on a pole tooth surface does not occur abruptly.During the rotation of the rotor, a rotor point should ideally experience neither an abrupt increase nor an abrupt decrease in magnetic flux density.

[0053] According to the invention, the permeability of the material of the pole tooth is thus distributed along the circumferential direction such that the permeability, at least adjacent to the pole tooth surface, in a section of the pole tooth near one pole tooth side surface or the two pole tooth side surfaces, is lower than with respect to the circumferential direction in a center of the pole tooth.

[0054] Both of the aforementioned measures, namely the formation of one or two protrusions as well as a variation of the permeability along the polar tooth surface, which can be increased by the protrusion(s), can be used together to achieve this effect of the smoothest possible increase and decrease in flux density towards the edges of the polar tooth.

[0055] The permeability of the material can preferably decrease in the circumferential direction towards the edges, i.e. towards the pole tooth side surfaces, and thus be greater in the middle of the pole tooth surface than at the pole tooth side surfaces or than in the projection or than in the projections.

[0056] In one possible embodiment, the variation in permeability can be achieved by arranging at least two materials, each with different permeability values, for example, circumferentially. For example, the two materials can comprise SMC and / or a ferrite and / or iron. Preferably, the two materials have a relative permeability µr greater than 1, for example, µr = 100, µr = 1000, or even greater, with one of the two materials having a lower relative permeability compared to the other. Preferably, the material with the lower relative permeability is arranged circumferentially closer to the pole tooth face than the other material.

[0057] For the sake of simplicity, the material of the pole tooth will be referred to as the first material and the material in the recess(s) as the second material. It is expressly noted here that the first material may be inhomogeneous with respect to its magnetic properties, particularly with respect to the circumferential direction of the pole tooth. The first and second materials can, in a combined effect with respect to the position of one or more recesses in the pole tooth, influence the conduction of the magnetic flux in the pole tooth and thus achieve an effective effect on the conduction of the magnetic flux in the pole tooth, which is equivalent to a variation in the permeability of the pole tooth. One or more recesses can be formed. Each of the recesses can be individually designed with respect to its dimensions, position, shape, and magnetic properties.

[0058] The invention therefore provides that the pole tooth has one or more recesses, each of which is filled with a material that differs from a surrounding material of the pole tooth at least with regard to permeability.

[0059] The recess in the pole tooth can be created, for example, using a 3D printing process or machining methods such as drilling, grinding, milling, laser cutting, punching, or etching.

[0060] It is possible that, in one embodiment, the recess has a maximum diameter of less than 0.5 mm, preferably less than 1 mm, more preferably less than 5 mm, and particularly preferably less than 10 mm. The advantage of using one or more such small recesses is that the effect of adjusting the effective permeability can be finely tuned, especially when multiple recesses are formed. A further advantage is that the mechanical stability of the pole tooth with the recess(s) is only slightly weaker than without the recess(s). This advantage is particularly effective when the recess(s) consist of inclusions of foreign material or filled cavities.It is conceivable that a pole tooth comprises one or more areas with at least 20 recesses each, preferably at least 10 recesses, and particularly preferably at least 2 recesses.

[0061] Different pole teeth in the stator of an active magnetic bearing can be designed differently in order to compensate for forces acting on the bearing or its components, such as the rotor, that are not radially symmetric. The force of gravity, for example, represents such a non-radially symmetric force.

[0062] In another embodiment, for example, in a laminated stator structure, the variation in permeability can also be configured as one or more recesses, wherein the one or more recesses are configured as one or more recesses in a sheet. The stator can comprise several sheets. A sheet can, for example, comprise iron, electrical steel, SMC, and / or a ferrite. Each of the one or more recesses can be individually configured with respect to its dimensions and magnetic properties. A second material, for example, air or a material that differs from the material of the sheet at least with respect to its magnetic properties, such as permeability, can be arranged in the one or more recesses of the sheet.

[0063] The one or more recesses in the sheet metal can, for example, comprise a recess that passes completely through the sheet metal or a recess that does not pass completely through it, wherein each of the one or more recesses has an opening with an area in the surface of the sheet metal. It is possible for the area of ​​the opening in the surface of the sheet metal to be less than 0.05 mm², preferably less than 1 mm², and particularly preferably less than 10 mm². The advantage of using such a small opening and a correspondingly small recess is that the effect for setting an effective permeability can be adjusted very precisely, especially, but not exclusively, when a plurality of such recesses are formed in one or more regions of the pole tooth.A further advantage is that the mechanical stability of the pole tooth is only slightly weaker with such a small opening and correspondingly small recess than without a recess. It is conceivable that one or more areas of the pole tooth with recesses comprise at least 20 recesses, preferably at least 10 recesses, and particularly preferably at least 2 recesses. In another embodiment, it is conceivable that the majority of such recesses comprise at least 20 recesses, preferably at least 10 recesses, and particularly preferably at least 2 recesses in a sheet of a pole tooth. The one or more recesses can be produced using a laser, 3D printing, or machining processes such as drilling, grinding, milling, punching, or etching.

[0064] Particularly in a stator or pole tooth constructed from several sheets stacked axially, each sheet can have one or more recesses for each pole tooth. The recesses of the majority of the sheets can connect axially, so that recesses form in a pole tooth that penetrate several sheets completely or partially. However, the recesses in the majority of the sheets can also be positioned differently or identically from sheet to sheet, and can also differ or be identical in shape, penetration, and / or penetration depth.

[0065] Preferably, the recesses are symmetrically formed or distributed within a plane that bisects a pole tooth in the axial direction. This avoids or at least reduces axial forces acting on the pole tooth.

[0066] Furthermore, the recesses in a pole tooth can be symmetrical with respect to a radial center plane that passes through the pole tooth in the radial direction. This can offer manufacturing advantages. Conversely, the recesses in a pole tooth can also be asymmetrical with respect to a radial center plane that passes through the pole tooth in the radial direction. This advantageously provides an additional degree of freedom in optimizing the gradient of the magnetic flux density at the pole tooth's side faces.

[0067] The method stipulates that when varying the material, the local permeability of the pole tooth is changed differently depending on its position, for example, depending on its position along the circumferential direction. This results in one or more gradients in the values ​​of the radial component of the magnetic flux density.

[0068] One embodiment provides that the one or more recesses are formed adjacent to the pole tooth side surfaces.

[0069] Preferably, the one or more recesses are filled with one or more materials that have a lower permeability than the surrounding material of the pole tooth. Different recesses can have different shapes and different fillings.

[0070] Other embodiments may have recesses only in a central area relative to the circumferential direction of the pole tooth. These are then preferably filled with a solid material that has a higher permeability than the surrounding material from which the pole tooth is formed. Here, too, the recesses can have different shapes and different fillings. In this way, a gradient of the radial component of a magnetic flux can also be generated during operation of the active magnetic bearing with respect to the circumferential direction. The radial component decreases towards the edges or pole tooth side faces.

[0071] The stator is designed, for example, such that a section of at least one winding is arranged in the pole gap to generate the magnetic flux density in the pole tooth when the at least one winding is energized. The winding can be used to generate the magnetic flux density in the pole tooth. The winding can be conventionally wound from a single wire. Other embodiments provide for the winding and its components to be produced by 3D printing or casting.

[0072] The model is preferably provided as a finite element model. This allows for very good and flexible modeling of both the geometry of the pole tooth and the other components of the stator or active magnetic bearing, as well as the materials used and their properties. For example, the permeability of the individual components, especially the radial permeability, can be modeled. Both the pole tooth and, for example, a support element can thus be modeled very accurately and precisely. Furthermore, granulation can be easily adjusted.

[0073] One embodiment of the method provides that the process step of calculating an evaluation function comprises the following steps: i) Calculating a Fourier coefficient for a high spatial frequency and a Fourier coefficient for a low spatial frequency from the profile of the magnetic flux density in the radial direction at the surface of the rotor in the circumferential direction, ii) Calculating a characteristic value that includes a ratio between the Fourier coefficient for the high spatial frequency and the Fourier coefficient for the low spatial frequency and / or a weighted sum of a power of the Fourier coefficient for the low spatial frequency and / or a power of the Fourier coefficient for the high spatial frequency, includes.

[0074] For example, modeling can be used to determine a radial flux density function BR(x), which represents the radial component of the magnetic flux density on the side of the rotor facing the pole tooth as a function of the circumferential position x in the recording. Fourier coefficients can be determined by performing a spatial Fourier transform of the radial flux density function. The resulting Fourier coefficients can be categorized as high-frequency (HF) Fourier coefficients and low-frequency (LF) Fourier coefficients, depending on their corresponding frequencies. Both the low and high frequencies can be interpreted as spatial frequencies, since the radial flux density function exhibits a spatially dependent behavior.When calculating the evaluation function, a Fourier coefficient ratio FV can be determined by calculating the ratio of the sum of the absolute values ​​of the high-frequency (HF) Fourier coefficients to the sum of the absolute values ​​of the low-frequency (LF) Fourier coefficients. Minimizing the Fourier coefficient ratio FV optimizes the stator or the active magnetic bearing.

[0075] The Fourier coefficients associated with high spatial frequencies, i.e., the RF Fourier coefficients, are linked to abrupt changes in the radial component of the magnetic flux density. Therefore, a reduction in the ratio of the sum of the absolute values ​​of the RF Fourier coefficients to the sum of the absolute values ​​of the LF Fourier coefficients correlates with a reduction in the eddy currents generated in the rotor, particularly in its lamination stack. This method thus optimizes the active magnetic bearing with respect to the power losses incurred during operation. The method therefore improves the design of the stator pole tooth(s) to achieve a reduction in eddy current losses.

[0076] A characteristic value that contains a weighted sum of a power of the Fourier coefficient for the low spatial frequency and / or a power of the Fourier coefficient for the high spatial frequency can be formed, for example, with: Loss = ∑ k = 1 K m a F jk 1.5 T 2 ⋅ f k 50 Hz 2 ⋅ σ w , 50 + f k 50 Hz ⋅ σ h , 50 , where Loss can be associated with the loss as a characteristic parameter, and where ma denotes the mass of a considered rotor section, fk = k·N / 60 with N as rotational speed in revolutions per minute indicates a frequency, and F(jk) indicates the respective Fourier coefficient assigned to fk, which is determined from the spatial Fourier transform of the radial flux density function of exactly one complete revolution around the rotor. j is the imaginary number. The material constant σw is an eddy current loss coefficient, and the material constant σh is a hysteresis coefficient. Both material constants must be chosen according to the material used or to be used for manufacturing. The index limit K allows selection of which frequency components are considered. This calculation formula is merely an example.For example, powers other than 2 can be chosen, individual frequencies can be omitted from the sum, and other material properties that need to be considered are also conceivable.

[0077] The procedure step of calculating the evaluation function can also include the step of calculating the local derivative of the magnitude of the magnetic flux density in the radial direction at the surface of the rotor.

[0078] Alternatively or additionally, calculating the evaluation function can include the step of calculating an average value of a function of the local derivative of the magnetic flux density in the radial direction at the surface of the rotor along a path length in the circumferential direction, i.e., the radial flux density function. Minimizing this average value also leads to a reduction in eddy current losses in the rotor due to abrupt changes in magnetic flux density.

[0079] Further training includes the calculation of the evaluation function, taking into account at least one additional parameter of the active magnetic bearing, particularly one that occurs during operation, and the determination of an extreme value of the evaluation function, taking into account a target value of at least one parameter.

[0080] Firstly, the size may refer to mechanical specifications, such as a minimum distance between adjacent pole teeth or similar specifications.

[0081] On the other hand, the size could also refer to, for example, the force acting on the rotor. A minimum value might be specified for this, to ensure the active magnetic bearing operates correctly.

[0082] One embodiment therefore provides that at least one quantity is an acting force. For example, this could be the force generated by the magnetic bearing, which serves to support the rotor. In this case, the force would correspond to the weight of the rotor.

[0083] In order to vary the permeability in the pole tooth, the invention provides that, when varying the permeability of the pole tooth material in the model, one or more recesses are arranged in the pole tooth which are filled with a material that differs from a surrounding material of the pole tooth at least with regard to permeability.

[0084] The invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 a section of a schematic drawing of a prior art active magnetic bearing; Fig. 2 a schematic diagram of the magnetic flux density in a radial direction along a circumferential direction of a prior art stator with pole teeth; Fig. 3 a section of a schematic drawing of an active magnetic bearing with a pole tooth having projections on the pole tooth side faces; Fig. 4 a schematic diagram of the magnetic flux density in the radial direction along a circumferential direction of a stator with pole teeth having projections on their pole tooth side faces; Fig. 5 a section of a schematic drawing of an active magnetic bearing with a pole tooth having projections on the pole tooth side faces and support elements; Fig. 6 a section of a schematic drawing of an active magnetic bearing with a pole tooth and another adjacent pole tooth whose projections are in contact with each other; Fig.6a a section of a schematic drawing of an active magnetic bearing with a pole tooth having recesses for varying a permeability in the circumferential direction; and Fig. 7 a schematic flowchart of a method for producing a stator of an active magnetic bearing or the active magnetic bearing itself.

[0085] Identical technical features are indicated in all figures with the same reference symbols.

[0086] In Fig. 1 Figure 1 shows an excerpt of a schematic representation of an active magnetic bearing 100 according to the state of the art, which has already been explained above in the introductory description.

[0087] Shown is a section of an active magnetic bearing 100. An axial receptacle 8 is formed in a stator 2, in which a rotor 1 is arranged. The stator 2 has several pole teeth 4. Each pole tooth 4 has a pole tooth surface 17 that partially delimits the axial receptacle. The rotor 1 is spaced from these pole tooth surfaces 17, and thus from the pole teeth 4, by a gap 3. A pole gap 5 is formed between each pair of adjacent pole teeth 4. The surfaces of the pole teeth 4 facing the pole gaps 5 are referred to here as pole tooth side surfaces 18a, 18b. In the embodiments according to the prior art, as in Fig 1 As shown, the pole tooth side surfaces 18a, 18b adjacent to the pole tooth surfaces 17 are planar and flat, for example parallel to a radial direction 11.

[0088] Preferably, one or more electrical conductors (not shown) are located in the pole gaps 5, each forming a winding around the pole tooth 4. The winding is thus formed by at least one electrical conductor that runs through the adjacent pole gaps 5 and surrounds the pole tooth 4 above and below the plane of the drawing.

[0089] When a current flows through the winding, a magnetic field is generated in the pole tooth, which typically comprises a soft magnetic material with very good magnetic conductivity and can, for example, be designed as a stack of laminations. In the prior art embodiment, a radial component of the magnetic flux density of the magnetic field is almost constant along a circumferential direction 12 on a pole tooth surface 17 facing the rotor 1. In the pole gap 5, the magnitude of the radial component of the magnetic flux density drops abruptly, usually to zero or almost zero, and then rises abruptly again in the region of the adjacent pole tooth 4.

[0090] In Fig. 2 schematically, a graph 30 of a radial component of the magnetic flux density 31 as a function of a position 32 along the circumferential direction 12 in the axial receptacle 8 of the stator 2 (compare Fig. 1) according to the prior art. Graph 30 thus indicates the radial component of the magnetic flux density 31 experienced by a rotor point 21 at the various positions during the rotation of the rotor 1. The position of the rotor point 21 can be specified as an angular position or as a length, measured along the path traversed by the rotor point during the rotation of the rotor 1. Shown is the radial magnetic flux density 31 occurring at a distance from the stator 2 corresponding to the gap 3 between the pole tooth surface 17 of one of the pole teeth 4 facing the rotor 1 and the rotor 1. Here, it is assumed that the stator surface of the axial receptacle 8 corresponds to an inner cylindrical surface, sections of which are formed by the central sections 24 of the pole tooth surfaces 17.

[0091] During a complete rotation of the rotor 1, the rotor point 21 sweeps across the area in the embodiment according to Fig. 2A total of eight pole teeth, 4-1 to 4-8 (not all shown). Their midpoints (also referred to as positions) are 14-1 to 14-8 in Fig. 2 The natural numbers trailing "-x" indicate an indexing of the pole teeth in a stator. The windings enclosing the corresponding pole teeth 4-1 to 4-8 are energized during operation such that a negative magnetic flux density is detected across the first pole tooth 4-1 and the fourth pole tooth 4-4, i.e., at positions 14-1 and 14-4, which is constant across the entire pole tooth extent. The pole teeth 4-2 and 4-3 at positions 14-2 and 14-3 generate a positive magnetic flux density. The windings of the remaining pole teeth 4-5 to 4-8 at positions 14-5 to 14-8 are only minimally energized or not energized at all.

[0092] When the rotor point 21 passes one of the pole tooth side faces 18a-n, 18b-n at positions 28a-n, 28b-n (n = 1, 2, ..., 4), the magnetic flux density rises or falls abruptly, in the illustrated embodiment according to the prior art by more than 90% of the magnitude of the maximum magnetic flux density 33 or minimum magnetic flux density 34. This abrupt change in magnetic flux density causes eddy currents in the rotor lamination stack 1a of the rotor 1, which lead to heating of the lamination stack 1a. These eddy currents thus represent significant losses that occur during the operation of the active magnetic bearing 100. These losses are proportional to the derivative of the radial component of the magnetic flux density.

[0093] In Fig. 3A schematic section of an active magnetic bearing 1000 is shown, in which the pole tooth side surfaces 18a, 18b of the pole teeth 4 are each formed with projections 6 adjacent to the pole tooth surfaces 17. These projections extend into the pole gap 5 between adjacent pole teeth 4. The projections 6 extend beyond the pole tooth side surfaces 18a, 18b, which extend radially inwards into the stator 2. These projections widen the respective pole tooth 4 towards the adjacent pole gap 5 and define and narrow the pole gap towards the rotor 1, or partially span the pole gap. The projections 6 are each formed from a magnetically conductive material. The projections 6 can be, as shown in Fig. 3 shown to be formed integrally with the rest of the pole tooth 4.

[0094] In Fig. 4 is analogous to Fig. 2a graph 30 of the magnetic flux density 31 as a function of the position 32 along the circumferential direction 12 in the axial recording 8 of the stator 2 (compare Fig. 3 ) shown.

[0095] Except for the projections 6, the embodiment is similar to the Fig. 3 according to the embodiment Fig. 1 according to the state of the art and the in Fig. 4 The depicted situation of the active magnetic bearing 1000 of the in Fig. 2 The operating situation of the active magnetic bearing 100 shown is based on the state of the art.

[0096] An amount 360 of the radial component of the magnetic flux density at the center positions 14-1 to 14-4 is slightly different from the amount 36 of the radial component of the magnetic flux density at the corresponding positions 14-1 to 14-4 in graph 30 of the prior art embodiment. Fig. 2lower. However, it is clearly noticeable that the radial component of the magnetic flux density 31, when sweeping over one of the positions 28a-n, 28b-n (n = 1, 2, ..., 4) of the pole tooth side surfaces 18a-n, 18b-n, the drop or rise of the magnetic flux density 31 is not as abrupt as in the embodiment according to the prior art. Figs. 1 and 2 The positions 28a-n, 28b-n are determined by extrapolating the flat, planar sections without the projections 6 of the pole tooth side surfaces 18a-n, 18b-n onto the surface of the rotor 1. They thus correspond to the positions 28a-n, 28b-n of the embodiment according to Figs. 1 and 2 .

[0097] Accordingly, the derivative dB R (x) / dt of the flux density curve BR (x) is smaller in magnitude at the edges of the swept pole teeth 4, i.e. at the pole tooth side surfaces, so that the generated eddy currents and thus the losses are also lower.

[0098] In Fig. 5is a further development of the embodiment according to Fig. 3 As shown, in this embodiment, support elements 7 are formed which absorb forces acting on the projections 6. As shown, the support elements 7 preferably bear in a form-fitting manner against the projections 6 on a side 26 of the corresponding projection 6 facing away from the rotor 1. The support elements 7 thus project into the bollard gaps 5.

[0099] The support elements 7 are preferably made of a material with poor magnetic conductivity or that is magnetically non-conductive. In particular, the material from which the support elements 7 are formed has a lower magnetic conductivity than the material from which the projections 6 are formed. The addition of the support elements 7 thus has no or virtually no influence on the formation of the radial component of the magnetic flux density.

[0100] In addition to the mechanical stabilization of the projections 6, the support elements 7 can also absorb thermal loads and thus preferably be in thermal contact with the corresponding projection 6 and / or the adjacent remainder of the pole tooth 4.

[0101] Furthermore, it is possible for the support element 7 and the projection 6 to be manufactured as a single piece, for example, using a 3D printing process. In addition, it is possible to implement a transition in permeability between the projection and the support element 7 in small steps. In extreme cases, these small steps can even result in a continuous transition in permeability.

[0102] In Fig. 6Another embodiment of the pole teeth 4 is shown. In this embodiment, the projections 6 of adjacent pole teeth 4 span the entire pole gap 5 between these pole teeth 4. The shape of the projections 6 is designed such that no magnetic short circuit occurs. In some embodiments (not shown), the mechanical contact between the adjacent projections 6 is formed via the support element or another connecting element, which is made of a magnetically poorly conductive material.

[0103] In other embodiments, the magnetic permeability of the pole tooth material can be varied, either alternatively or cumulatively, in addition to forming projections or generally modifying the geometry. For example, the pole teeth can be designed such that the magnetic permeability decreases towards the pole gaps or the pole tooth side surfaces. The pole tooth is preferably designed such that the magnetic permeability varies, preferably at least adjacent to the pole tooth surface 17. In this case, the permeability decreases towards the pole gaps.

[0104] However, the permeability of the material can also exhibit a variation in magnetic permeability, particularly in the radial component, within the interior, i.e., at a distance from the pole tooth face. Here too, the permeability adjacent to the pole tooth faces is preferably lower than at a midpoint between the pole tooth faces.

[0105] Figure 6aFigure 1 schematically shows a configuration of a pole tooth 4 with several recesses 9. The number, size, shape, and / or arrangement of the recesses 9 can vary. As shown in Figure 2. Figure 6a As shown, several recesses 9 are formed adjacent to the pole tooth side faces 18a, 18b. These recesses penetrate the pole tooth 4 completely in the axial direction, for example. In other embodiments, where the stator 2 is formed from axially stacked laminations, the recesses may only be formed in individual laminations. The recesses may be configured differently, particularly in the laminations. The sizes and arrangement of the recesses 9 are shown only as examples.

[0106] The recesses are not uniformly distributed in the circumferential direction 12 of the pole tooth 4. Preferably, they are adjacent to the pole tooth side faces and, by way of example in this illustration, symmetrically formed with respect to a central plane 20 of the pole tooth 4. Other embodiments may only provide recesses in a center 20a of the pole tooth 4 with respect to the circumferential direction 12. The aim is to generate a gradient, preferably a low one, of the radial component of a magnetic flux during operation of the active magnetic bearing 1000 with respect to the circumferential direction.

[0107] The pole tooth can comprise a first material 9a. Each of the recesses is filled with a material 9b, which, without loss of generality, is referred to here as the second material, and which differs from the surrounding material 9a of the pole tooth, referred to here as the first material. The first material 9a and the second material 9b differ with respect to their magnetic properties, in particular their permeability. For example, the first material 9a can be iron or electrical steel, and the second material 9b can, for example, comprise air. However, the second material 9b can also be any other material that differs from the first material. If several recesses 9 are formed in a pole tooth, they can all contain the same second material 9b. However, it is also possible to fill the different recesses 9 with different second materials 9b.This offers the possibility of optimally influencing the permeability of the pole tooth. A single recess can also be filled with two different second materials 9b, for example, if the recess 9 is partially filled with a second solid and partially with air.

[0108] The recesses are preferably closed off from the pole tooth surface and the pole tooth side surfaces 18a, 18b. This applies in particular if the recess is not filled with a solid as a second material 9b.

[0109] In Figure 6aIt has been shown that the recess 9 in the pole tooth 4 is located near the pole gap 5. This allows the magnetic flux density in the pole tooth to be guided differently, i.e., better or worse, in a region near the pole gap 5 than, with respect to the circumferential direction, at a center 20a of the pole tooth 4. This is equivalent to a variation in the permeability in the pole tooth in terms of its effective effect.

[0110] Here, a position, an extent, a shape and the second material 9b of the recess 9 are to be designed such that the magnetic flux density in a region of the pole tooth 4 near the pole gap 5 is directed differently than, with respect to the circumferential direction, in a region around the center 20a of the pole tooth 4.

[0111] Each of the recesses 9 can be individually designed with respect to its extent, for example, a maximum extent in the circumferential direction and / or the radial direction, and the second material 9b. Both the extent, the second material 9b, and the position of the recess 9 in the pole tooth 4 can be used as part of a model or as a parameter thereof in the claimed method for forming a stator 2. Recesses 9 with a circular cross-section are particularly preferred, as these are easy to manufacture.

[0112] In Fig. 7 The flowchart shown is a schematic example of the process for generating an active magnetic bearing or a stator for an active magnetic bearing.

[0113] First, a model is provided or created. This preferably comprises sub-models that model at least one pole tooth of a stator, sections of adjacent pole gaps, and a section of a rotor, as well as a gap between the rotor and stator, and the generation of a magnetic flux density in the pole tooth. The pole tooth model 6 models its geometric shape, preferably in form and dimensions, and / or the magnetic permeability of the pole tooth material. The model may include sub-models for other components such as support elements, windings, etc. Preferably, the model is provided or created as a finite element model.

[0114] Based on the model, a magnetic flux density at the rotor surface in the radial direction is calculated as a function of the circumferential position. For the modeled shape of the pole tooth, a radial flux density function BR(x) is preferably calculated, which specifies a radial component of the magnetic flux density at a side of the rotor facing the stator as a function of the circumferential position x in the axial receptacle of the stator. Preferably, the entire stator or the entire magnetic bearing is described by the model, and the radial flux density function is calculated circumferentially around the stator for an operating condition in which the bearing actively holds the rotor. In this case, models can often be greatly simplified due to symmetry considerations.

[0115] Based on this, an evaluation function 2300 is calculated, which evaluates a measure of losses occurring in the rotor depending on changes in the magnitude of the magnetic flux density in the radial direction on the surface of the rotor along a path in the circumferential direction.

[0116] The procedure step of calculating the valuation function can include different sub-steps, which are listed below.

[0117] In one embodiment, calculating the evaluation function includes determining Fourier coefficients for at least one low spatial frequency and for at least one high spatial frequency for the radial flux density function 2310 calculated on the basis of the modeling.

[0118] Determining the Fourier coefficients can be done, for example, by performing a Fourier transformation, preferably in the form of a Fast Fourier transformation 2315.

[0119] Fourier coefficients corresponding to high spatial frequencies can be associated with abrupt changes in magnetic flux density in the radial direction. Consequently, large Fourier coefficient values ​​for high spatial frequencies are associated with high losses in the rotor's laminated core.

[0120] In order to associate the absolute values ​​of the Fourier coefficients for high spatial frequencies with such losses, it may be necessary to relate them to the absolute values ​​of Fourier coefficients for low spatial frequencies.

[0121] One embodiment of the method therefore provides for the evaluation of a weighting function that depends on the Fourier coefficients. For example, a ratio can be formed between Fourier coefficients for high spatial frequencies and Fourier coefficients for low spatial frequencies. In some embodiments, only a Fourier coefficient for a high spatial frequency is related to a Fourier coefficient for a low spatial frequency.

[0122] In another embodiment, a sum of the Fourier coefficients for high spatial frequencies is compared to a sum of the Fourier coefficients for low spatial frequencies. In other embodiments, a weighted sum of the Fourier coefficients or of powers of the Fourier coefficients is calculated.

[0123] In another embodiment, calculating the evaluation function includes differentiating the radial flux density function 2330. If abrupt changes occur in the radial flux density, the derivative will have large magnitudes. If the change in the radial flux density is less abrupt, for example due to protrusions in the pole tooth side faces, the magnitudes of the derivative will be smaller.

[0124] One embodiment therefore provides that calculating the evaluation function includes calculating a function as a function of the values ​​of the derivative of the radial flux density. For example, an average of the absolute values ​​of the derivative can be performed.

[0125] In other embodiments, at least one further parameter is determined based on the modeling and taken into account in the calculation of the evaluation function 2340.

[0126] The size may, for example, be a mechanical requirement, such as a minimum distance between adjacent pole teeth or similar specifications.

[0127] On the other hand, the size could also refer to, for example, the force acting on the rotor. A minimum value might be specified for this, to ensure the active magnetic bearing operates correctly.

[0128] According to step 2400, the model or one of its parameters is varied. For example, the geometric shape of the pole tooth and / or the material of the pole tooth and its properties, especially its magnetic permeability, can be varied. Likewise, the shape of a support element and its material, etc., can be varied.

[0129] Steps 2200 to 2400, including any sub-steps up to 2500, are iterated to optimize the evaluation function, i.e., to find an extreme value of the evaluation function, possibly subject to boundary conditions. Typically, the extreme value will be a minimum value.

[0130] If an optimization has taken place, information about the stator corresponding to the extreme value of the evaluation function, in particular about at least one pole tooth, is output 2600.

[0131] This information is then used to create a stator or an active magnetic bearing with such a stator 2700.

[0132] It will be understood by those skilled in the art that only exemplary embodiments are given. The invention is defined by the appended claims. Reference sign

[0133] 1 Rotor 1a Rotor lamination stack 2 Stator 3 Gap 4, 4-x Pole tooth 5 Pole gap 6 Projection 7 Support element 8 Axial mount 9 Recess 9a (First) material of the pole tooth 9b Different (Second) material, for filling the recess 10 Rotation axis 11 Radial direction 14, 14-x (Center) position 17 Pole tooth surface 18a, 18b Pole tooth side faces 19 Center of the pole tooth surface 20 Center plane 20a Center 21 Rotor point 24 Middle section of the pole tooth surface 26 Side of the projection facing away from the rotor 28a-x,28b-x Positions of the pole tooth side faces 30 Graph 31 Radial component of the magnetic flux density 32 Position along the circumferential direction 33 Maximum magnetic flux density 34 Minimum magnetic flux density 36 Magnitude of the radial component of the flux density 360 Magnitude of the radial component of the flux density 100 State-of-the-art active magnetic bearing 1000 Active magnetic bearing 2000 Flowchart 2100 Provision / Creation of a model 2200 Calculation of the magnetic flux density 2300 Calculation of an evaluation function 2310 Determination of Fourier coefficients 2315 Performance of a fast Fourier transform 2320 Calculation of an evaluation function,which depends on the Fourier coefficients 2330 Derivation of the radial flux density function 2335 Averaging of the derivative of the radial flux density function 2340 Determining at least one further quantity and calculating the evaluation function depending on the further quantity 2400 Varying the model 2500 Iterating process steps to optimize the evaluation function 2600 Outputting information about the modeled stator 2700 Manufacturing a stator or active magnetic bearing based on the information,

Claims

1. A stator (2) of an active magnetic bearing (1000) - comprising an axial receptacle (8) for a rotor (1) spaced apart from the stator (2) by a gap (3), which is configured to conduct a magnetic flux density and to rotate about an axis of rotation arranged in an axial direction perpendicular to a cross-sectional area of the axial receptacle (8) - comprising a pole tooth (4), which comprises a pole tooth surface (17), which forms a circumferential section of the axial receptacle (8), and two pole tooth side surfaces (18a, 18b) which delimit the pole tooth (4) in a circumferential direction (12), oriented perpendicular to the axial direction, on both sides respectively against a respective adjacent pole gap (5), wherein the pole tooth (4) is configured to conduct the magnetic flux density such that, at a centre (19) of the pole tooth surface (17), the outgoing or incoming magnetic flux density exhibits a maximum magnitude in a radial direction (11) which is oriented perpendicular to the axial direction and perpendicular to the circumferential direction (12), and - wherein a material of the pole tooth (4) exhibits an inhomogeneity of permeability relative to the circumferential direction (12) - wherein the permeability of the material of the pole tooth (4) is distributed along the circumferential direction (12) such that the permeability, at least in an area adjacent to the pole tooth surface (17), in a section of the pole tooth (4) near one pole tooth side surface or both pole tooth side surfaces (18a, 18b), is lower than at a centre of the pole tooth (4) relative to the circumferential direction (12) - characterised in that the pole tooth (4) comprises one or more recesses (9), each of which is filled with a material (9b) that differs from a surrounding material (9a) of the pole tooth (4) at least with respect to permeability, wherein the one or more recesses are each formed as cavities enclosed by the material of the pole tooth at least in planes oriented perpendicular to the axial direction, spaced apart from the pole tooth surface and optionally from the pole tooth side surfaces.

2. A stator (2) of an active magnetic bearing (1000) according to claim 1, characterised in that, in addition to the inhomogeneity of the material's permeability, one or both pole tooth side surfaces (18a, 18b) adjacent to the pole tooth surface (17) facing the rotor (1) feature a projection (6) which tapers or spans the respective adjacent pole gap (5).

3. A stator (2) of an active magnetic bearing (1000) according to claim 2, characterised in that the projection (6) of one of the pole tooth side surfaces (18a, 18b) differs from a projection (6) of the respective other pole tooth side surface (18a, 18b) and / or a projection (6) of a pole tooth side surface (18a, 18b) of a further adjacent pole tooth (4) or of another pole tooth (4) with regard to a geometric dimension and / or the inhomogeneity of at least one radial component of the permeability.

4. A stator (2) of an active magnetic bearing (1000) according to one of claims 2 or 3, characterised in that a support element (7) for absorbing forces acting on the projection (6) is arranged on the projection (6) in the pole gap.

5. Stator (2) of an active magnetic bearing (1000) according to one of the preceding claims, characterised in that the one or more recesses (9) are formed adjacent to one or more pole tooth side surfaces (18a, 18b).

6. A stator (2) of an active magnetic bearing (1000) according to one of the preceding claims, characterised in that a section of at least one winding is arranged in the pole gap (5) to generate the magnetic flux density in the pole tooth (4) when the at least one winding is energised.

7. Active magnetic bearing (1000) comprising the stator (2) according to one of the preceding claims and the rotor (1), which is arranged in the axial receptacle (8) of the stator (2) spaced apart by the gap (3) and is configured to conduct the magnetic flux density and to rotate about the axis of rotation arranged in the axial direction, perpendicular to the cross-sectional area of the axial receptacle (8).

8. A method for forming a stator (2) of an active magnetic bearing (1000) according to any one of claims 1 to 8, or an active magnetic bearing (1000) according to claim 7, comprising the steps of: a) providing a model which models at least the pole tooth (4) with the pole tooth surface (17) and the pole tooth side surfaces (18a, 18b), at least sections of the adjacent pole gaps (5) and at least a section of the rotor (1) spaced apart by the gap (3), as well as the generation of the magnetic flux density in the pole tooth (4), b) calculating the magnetic flux density at the surface of the rotor (1) in the radial direction (11) using the model as a function of position in the circumferential direction (12), c) calculating an evaluation function that evaluates a measure of losses occurring in the rotor (1) as a function of changes in a magnitude of the magnetic flux density in the radial direction (11) at the surface of the rotor (1) along a path in the circumferential direction (12), d) varying a permeability of the material of the pole tooth (4) in the model, wherein, when varying the permeability of the material of the pole tooth (4) in the model, one or more recesses (9) are arranged in the pole tooth (4), which are filled with a material (9b) that differs from a surrounding material (9a) of the pole tooth (4) at least in terms of permeability, wherein the one or more recesses are each formed as cavities enclosed by the material of the pole tooth at least in planes oriented perpendicular to the axial direction, spaced apart from the pole tooth surface and optionally from the pole tooth side surface, e) performing the method steps b) to d) iteratively to determine an extreme value of the evaluation function g) Outputting information describing the pole tooth (4) according to the model, which corresponds to the determined extreme value of the evaluation function, and h) forming a stator (2) or an active magnetic bearing (1000) with a pole tooth based on the outputted information, which corresponds to the pole tooth (4) according to the model.

9. A method according to claim 8, characterised in that, additionally in step d), a geometric shape of the pole tooth (4), in particular of the pole tooth side surface (18a, 18b) adjacent to the pole tooth surface (17), is varied.

10. A method according to claim 8 or 9, characterised in that the model is provided as a finite element model.

11. A method according to any one of claims 8 to 10, characterised in that the method step of calculating an evaluation function comprises the steps of: i) calculating a Fourier coefficient for a high spatial frequency and a Fourier coefficient for a low spatial frequency from the profile of the magnetic flux density in the radial direction (11) at the surface of the rotor (1) in the circumferential direction (12), ii) calculating a characteristic value comprising a ratio between the Fourier coefficient for the high spatial frequency and the Fourier coefficient for the low spatial frequency and / or a weighted sum of a power of the Fourier coefficient for the low spatial frequency and / or a power of the Fourier coefficient for the high spatial frequency.

12. A method according to any one of claims 8 to 11, characterised in that the method step of calculating the evaluation function comprises the step of calculating a local derivative of the magnitude of the magnetic flux density in the radial direction at the surface of the rotor (1).

13. A method according to claim 12, wherein the method step of calculating the evaluation function comprises the step of calculating a mean value of a function of the local derivative of the magnetic flux density in the radial direction (11) at the surface of the rotor (1) along a path in the circumferential direction.

14. A method according to any one of claims 8 to 13, wherein a further parameter of the active magnetic bearing (1000) is additionally determined, and the determination of the extreme value of the evaluation function is carried out taking into account a predetermined value of the further parameter, wherein the further parameter is, in particular, a force.

15. A method according to any one of claims 8 to 14, characterised in that a position and / or a shape and / or an extent and / or the filling material (9b) of the one or more recesses (9) in the pole tooth (4) is varied.