CN113508512A

CN113508512A - Permanent magnet assembly comprising three magnet arrangements with different magnetic domain alignment patterns

Info

Publication number: CN113508512A
Application number: CN201980093925.6A
Authority: CN
Inventors: Z·阿扎尔; R·克拉克; H-J·图加德; A·C·乌尔达
Original assignee: Siemens Gamesa Renewable Energy AS
Current assignee: Siemens Gamesa Renewable Energy AS
Priority date: 2019-03-11
Filing date: 2019-08-30
Publication date: 2021-10-15
Also published as: WO2019219985A2; WO2019219985A3

Abstract

A permanent magnet assembly (360, 460) is described that includes a first side magnet arrangement (280 a), a second side magnet arrangement (280 b), and a center magnet arrangement (270, 470) therebetween. The central magnet arrangement (270, 470) has an angular spread of domain alignment directions (375, 475) that results in a focused magnetization that defines a focal point (377). The two side magnet arrangements (280 a, 280 b) have only single magnetic domain alignment directions (382 a, 382 b) resulting in parallel magnetization. The single magnetic domain alignment directions (382 a, 382 b) are tilted with respect to a magnetic axis (377 a) defined by a shortest distance between the focal point (377) and a major surface (270 a) of the central magnet arrangement (270, 470). Further described is a rotor assembly (150) with such a permanent magnet assembly (360, 460), an electromechanical transducer (140) with such a rotor assembly (150), and a wind turbine (100) with such an electromechanical transducer (140).

Description

Permanent magnet assembly comprising three magnet arrangements with different magnetic domain alignment patterns

Technical Field

The present invention relates to the field of permanent magnet technology with non-uniform magnetic domain alignment patterns. The invention further relates to a rotor assembly for an electromechanical transducer, comprising at least one such permanent magnet. Furthermore, the invention relates to an electromechanical transducer comprising such a rotor assembly and to a wind turbine comprising such an electromechanical transducer.

Background

Permanent magnetic materials are used in a number of different fields of application. Probably, the most technically and economically important fields of application are electromechanical transducers, i.e. motors and generators. An electric motor equipped with at least one Permanent Magnet (PM) converts electrical energy into mechanical energy by generating a temporally changing magnetic field by means of windings or coils. This temporarily varying magnetic field interacts with the magnetic field of the PM, causing, for example, a rotational movement of the rotor assembly relative to the stator assembly of the electric motor. In a physically complementary manner, a generator (also called a dynamic electrical machine) converts mechanical energy into electrical energy.

A generator is a core component of any power plant for generating electrical energy. This applies to power plants that capture mechanical energy directly, such as hydroelectric facilities, tidal power facilities and wind power facilities, also named wind turbines. However, this also applies to power plants which (i) firstly use chemical energy (for example from burning fossil fuels or from nuclear energy) in order to generate thermal energy and (ii) secondly convert the generated thermal energy into mechanical energy by means of suitable thermodynamic processes.

It is evident that the efficiency of the generator is likely to be the most important factor in optimizing the production of electrical energy. For PM generators, it is essential that the magnetic flux generated by the Permanent Magnets (PM) is strong. This is most likely to be best achieved with sintered rare earth magnets, for example using a FeNdB material composition. However, the spatial magnetic field distribution produced by the PM also has an effect on the generator efficiency. In the latter case, it is often advantageous to use PM devices or PM arrangements (arrangements) with non-uniform magnetic domain alignment patterns that result in intentionally non-uniform magnetic field strength or flux density, particularly in the air gap between the rotor and stator assemblies.

WO 2012/141932 a2 discloses PM magnet arrangements in which differently magnetized PMs are combined such that "magnetic focusing" is achieved. Differently magnetized PMs may be mounted on a common back plane, for example made of iron.

EP 3276642 a1 discloses a sintered rare earth PM having a focused magnetic alignment pattern achieved by an integrally formed or one-piece PM body.

EP 2762838 a2 discloses an apparatus and a method for manufacturing PMs, wherein during the sintering process a non-uniform external magnetic field is applied in order to magnetize different regions of the PM in different directions.

Magnetic domain alignment patterns, which form curved magnetization lines within the PM body, can also be generated by appropriate external magnetic fields.

WO 2009017430 a1 discloses a magnet device having magnetic domains that are not isotropically aligned so as to form a magnetic domain alignment pattern, wherein the direction of the corresponding magnetization direction changes substantially continuously from at least partially radially to at least partially tangentially across at least a portion of the magnet device between its lateral edges.

All of the above mentioned known PM and PM devices are not easy to manufacture as a suitable external non-uniform magnetic field is necessary in order to provide proper alignment of the magnetic domains.

It may be desirable to provide a PM assembly that can be easily manufactured and that in many applications contributes to an improved efficiency of the electromechanical transducer.

Disclosure of Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the invention are described by the dependent claims.

According to a first aspect of the present invention, there is provided a permanent magnet assembly comprising: a central magnet arrangement; a first side magnet arrangement arranged at a first side of the central magnet arrangement; and a second side magnet arrangement arranged at a second side of the central magnet arrangement. The provided permanent magnet assembly further comprises the following features:

(a) the central magnet arrangement is sandwiched between the first side magnet arrangement and the second side magnet arrangement.

(b) The central magnet arrangement has an angular distribution of expansion resulting in a domain alignment direction of the focusing magnetization, which defines a focal point,

(c) both the first side magnet arrangement and the second side magnet arrangement have only a single magnetic domain alignment direction resulting in parallel magnetization.

(d) The single magnetic domain alignment direction is tilted with respect to a magnetic axis defined by the shortest distance between the focal point and the main surface of the central magnet arrangement.

The described Permanent Magnet (PM) assembly is based on the following concept: a reasonable compromise between (i) the overall effort to produce the entire PM assembly, (ii) the strength of the magnetic flux generated by the PM assembly and (iii) the degree of magnetic focussing can be achieved by assembling three magnet arrangements in which only one magnet arrangement (i.e. the central magnet arrangement) comprises a non-uniform distribution of domain alignment directions leading to focussing magnetisation, and the other magnet arrangements comprise (typically) parallel magnetisation directions. In particular, it is only necessary to use a magnet arrangement (i.e. a central magnet arrangement) that is relatively complex and difficult to manufacture in order to ultimately become a PM component that produces a desired spatial distribution of (i) a sufficiently strong magnetic field or flux and (ii) a magnetic field (lines) or flux (lines) for many applications.

The term "magnetic axis defined by the shortest distance between the focal point and the main surface of the central magnet arrangement" may particularly mean that the magnetic axis is oriented perpendicular to (the plane of) the main surface of the central magnet arrangement and that the focal point lies on the magnetic axis. In this regard, the magnetic axis may be considered to correspond to the optical axis of a focusing optical element (e.g., a refractive lens). In this document, the term "magnetic domain alignment direction" may also be referred to as the magnetization direction within the block of the respective magnet arrangement.

It should be noted that the focus of the central magnet arrangement may not be perfect. Thus, the angular spread of the domain alignment direction may not produce a precise or sharp focus, but rather a (distributed) focus region around the desired precise or sharp focus.

According to an embodiment of the invention, the magnetic axis is an axis of symmetry of the central magnet arrangement, wherein the symmetry is given by the spatial shape and size of the central magnet arrangement and/or by the angular spread distribution of the domain alignment direction.

Constructing the central magnet arrangement in a symmetrical manner may provide the following advantages: compared to an asymmetric configuration, the central magnet arrangement can be manufactured relatively easily with known processes and apparatuses, for example to magnetize the central magnet arrangement unevenly during the sintering process.

According to a further embodiment of the invention, the magnetic axis is an axis of symmetry of the entire permanent magnet assembly, wherein the symmetry is given by the spatial shape and size of the entire permanent magnet assembly and/or by the overall distribution of the magnetic domain alignment directions.

Described symmetry of the entire PM assembly may mean that the two (outer) side magnet arrangements are mirror images of one another about the axis of symmetry, descriptively. This may be applicable to the spatial shape and size of the two side magnet arrangements and/or the single magnetic domain alignment direction of the two side magnet arrangements. This may provide the following advantages: the described PM component can be designed and implemented in a comparatively simple and efficient manner.

In a preferred configuration, the two side magnet arrangements are of the same type. Therefore, to build the described PM assembly, only two different types of magnet arrangements are necessary, namely a focused central magnet arrangement and a (doubly used) non-focused side magnet arrangement. When assembling the PM assembly, one of the two side magnet arrangements may simply be oriented in an inverted manner compared to the other of the two side magnet arrangements.

In this document, the term "overall distribution of magnetic domain alignment directions" may refer to the magnetic domain alignment distribution of or within all magnet arrangements of a magnet assembly comprising a central magnet arrangement and two side magnet arrangements. If the magnet assembly comprises additional magnet means, the "overall distribution of magnetic domain alignment directions" may also comprise a distribution of magnetic domain alignment magnetization directions in these additional magnet means.

The described mirror-symmetric PM assembly may provide the following advantages: it can be designed and manufactured even more easily than a PM assembly in which only the central magnet arrangement is symmetrical and the whole of the two outer magnet arrangements is asymmetrical.

According to a further embodiment of the invention, at least one of the central magnet arrangement, the first side magnet arrangement and the second side magnet arrangement is formed as a single magnet piece. This may provide the following advantages: three different magnet pieces are sufficient to realize the described PM assembly.

In the context of this document, the term "single magnet piece" may particularly mean that the respective magnet arrangement is integrally or monolithically formed by means of a single bulk material.

According to a further embodiment of the invention, at least one of the central magnet arrangement, the first side magnet arrangement and the second side magnet arrangement comprises at least two magnet pieces.

In this embodiment, at least one of the (at least) three magnet arrangements is composed of at least two single magnet pieces. This may provide the following advantages: the entire PM assembly and in particular the central magnet arrangement can be realized by composing or assembling smaller magnet pieces. Although some effort may be required to assemble different magnet pieces, in most cases this effort will be overcompensated because only smaller magnet pieces have to be produced. This is applicable because, especially for focusing magnet pieces, it is easier to manufacture two or more small focusing magnet pieces than one large focusing magnet piece.

Forming a magnet arrangement with at least two magnet pieces may provide advantages not only in terms of the manufacturing process of the magnet arrangement, but also in terms of the operational efficiency of a generator equipped with a "multi-piece" magnet arrangement. In this context, eddy currents generated within the body of the magnetic device due to the magnetic backtracking effect may be reduced. In particular, the time-varying current induced in the stator coils due to the time-varying magnetic field caused by the moving magnet arrangement results in a time-varying magnetic field generated by the respective stator coil. This time-varying magnetic field again causes eddy currents in the body of the magnet arrangement. It will therefore be appreciated that the interface between the different magnet pieces may provide a barrier to such eddy currents. The barrier may be reinforced when an electrically insulating medium (e.g. a non-conductive glue) is provided between the different magnet pieces.

According to a further embodiment of the invention, the two magnet pieces directly abut against each other.

A PM assembly with directly adjoining magnet pieces may provide the following advantages: the PM assembly can be implemented within a compact design. A further advantage may be that at the interface between two adjacent magnet pieces, there may be at least approximately no distortion of the magnetic flux lines. Such distortion of the flux lines will most likely occur if there will be a gap between the two respective magnet pieces.

In this document, the term "directly adjoining" may mean that there is no intended gap between the two magnet pieces. This means that: for example a small layer of adhesive and/or a surface protection or passivation layer between the actual magnetic materials of the two magnet pieces does not mean that the two magnet pieces do not abut directly against each other.

According to a further embodiment of the invention, at least one of the central magnet arrangement, the first side magnet arrangement and the second side magnet arrangement is a sintered magnet, in particular a sintered magnet comprising NdFeB.

It may be particularly advantageous to form the described PM assembly by means of different magnet arrangements, wherein each of these magnet arrangements may be formed by one or more (permanent) magnet pieces, when it is considered that the sintered magnets are typically of a very rigid and/or brittle structure such that further processing of the respective sintered magnet is not easy. This may be particularly applicable for magnets comprising typical NdFeB material compositions.

By using at least two relatively small sintered magnet arrangements or magnet pieces instead of one larger sintered magnet arrangement or magnet piece, the risk of mechanically damaging the magnet arrangements or magnet pieces during further processing can be significantly reduced. Such further processing may include, for example, a process of providing a protective layer at the outer surface of the magnet piece.

To avoid any misunderstanding in the (internal) magnetising structure of the sintered magnet, it should be noted that the magnetic domain alignment direction described above is based on or directly related to the preferred direction of grain orientation. This means that it is not necessary that all grains (contributing to a particular magnetic domain alignment direction or magnetization line) must be oriented exactly in the same direction. Rather, it is only necessary that, among a certain distribution of grain orientations, there be (on average) a preferred grain orientation.

According to a further embodiment of the present invention, the spread angle distribution of the magnetic domain alignment direction includes a straight line.

Having the focus magnetization direction along a straight line provides the following advantages: for example, during the sintering process, the process of manufacturing the central magnet apparatus may be facilitated. This is particularly suitable, since, in order to produce the magnetic domain alignment (pattern) of the central magnet arrangement, an external magnetic field with corresponding and necessary inhomogeneities can be generated comparatively easily by a suitable spatial arrangement of the external magnet coils. Preferably, all of the magnetic domain alignment lines within the central magnet arrangement are straight lines.

According to a further embodiment of the invention, the angular distribution of the expansion of the domain alignment direction (within the central magnet device) comprises curved domain alignment lines.

Providing curved or arcuate magnetic domain alignment lines may provide the following advantages: at the interface between the central magnet device and at least one of the two side magnet devices, there may be a smooth transition in the magnetic domain alignment direction or the orientation angle of the magnetic domain alignment lines. This may mean: at this interface, the difference between the angle of the curved magnetic domain alignment lines of the central magnet arrangement and the respective side magnet arrangements may be small. In a preferred embodiment, the angular difference is at least approximately zero. In other words, there is no (significant) step change in the orientation of the magnetic domain alignment lines at this interface.

A smooth transition in the orientation of the magnetic domain alignment lines may provide the following advantages: the magnetic field or flux focusing behavior of the central magnet arrangement towards the focal point will not be disturbed. This interference will result in an increased focal area. In contrast, the side magnet arrangement can significantly increase the magnetic strength of the entire magnet assembly, so that the strength of the magnetic field, particularly at the focal point, will be increased compared to a single-focus (central) magnet arrangement.

According to a further embodiment of the present invention, for the center magnet device, (a) a first angle at the main surface between (i) the magnetic domain alignment direction and (ii) the magnetic axis is smaller than (b) a second angle at an interface between (i) the magnetic domain alignment direction and (ii) the magnetic axis between the center magnet device and at least one of the two side magnet devices.

Descriptively, the described angular relationship may mean: with respect to the plane of the main surface, (i) the magnetic domain alignment direction of the magnetized lines "out" of the central magnet arrangement at the main plane is steeper than (ii) the magnetic domain alignment direction of the magnetized lines "in" the central magnet arrangement at the respective interfaces.

Preferably, the magnetization lines "entering" the central magnet arrangement at one interface and "leaving" the central magnet arrangement at a main surface are bent towards the "left-hand side", and the magnetization lines "entering" the central magnet arrangement at the opposite other interface and also "leaving" the central magnet arrangement at a main surface are bent towards the "right-hand side". This may provide the following advantages: it is also possible to implement a configuration in (mirror) symmetry with a central magnet arrangement having curved magnetic domain alignment lines.

According to a further embodiment of the present invention, for at least one of the first side magnet arrangement and the second side magnet arrangement, the tilt angle between the single magnetic domain alignment direction and the magnetic axis is in the range of 20 ° and 70 °, preferably in the range of 30 ° and 60 °, and more preferably in the range of 40 ° and 50 °. Most preferably, the described angle of inclination may be at least approximately 45 °.

The straight lines may be oriented such that they are inclined towards the magnetic axis. Thereby, in an advantageous manner, the magnetic focusing of the central magnet will be supported by the two side magnet arrangements.

According to a further embodiment of the invention, each of the magnet arrangements comprises a height and a width, wherein the height is measured in a direction parallel to the magnetic axis and the width is measured in a direction parallel to a common normal vector of the mutually facing side surfaces of the two side magnet arrangements. The described magnet assembly comprises at least one of the following features (a), (B) and (C):

characteristic (A): the central magnet arrangement comprises an aspect ratio in the range between 0.2 and 1.0, in particular between 0.4 and 1.0, and more in particular between 0.6 and 1.0.

Thus, the aspect ratio is defined by the ratio between the height and the width of the central magnet arrangement.

With respect to feature (a), the inventors have found that the proper aspect ratio of the focused central magnet arrangement may have a significant impact on the magnetic flux that may be achieved within the air gap of the generator. In particular, by contrast to non-focusing magnet arrangements, which are typically sized by machine designers at a minimum height (particularly for cost reasons), focusing magnet arrangements can provide significantly higher efficiency to generate strong magnetic flux. This significantly higher efficiency may be the reason for designing the focusing magnet arrangement to have a larger magnet volume, which is of course associated with more cost or expense of the necessary magnet material.

At least for generators suitable for wind turbines, the width of the central magnet arrangement may be in the range between 25 mm and 200 mm, and in particular between 50 mm and 100 mm. In this regard, the inventors have further discovered that the optimal aspect ratio may depend on the absolute value of the width. For example, for a magnet arrangement having a width of 50 mm, a beneficial aspect ratio may be in the range between 0.4 and 0.8. For a magnet arrangement with a width of 100 mm, an advantageous aspect ratio may be in the range between 0.2 and 0.6. Among these considerations, the cost of the magnetic material may also be taken into account.

Feature (B): the height of the central magnet arrangement is different, in particular greater, than the height of at least one of the side magnet arrangements.

With regard to feature (B), the inventors found that in the case of the described non-uniform height of the permanent magnet assembly, the (upper) surface of the permanent magnet assembly can be approximated by a curved (sinusoidal) surface, which can be spatially shaped in this way, modifying the magnetic flux density accordingly (in particular within the air gap between the rotor assembly and the stator assembly), so that a smooth operation of the corresponding electromechanical transducer (small cogging torque, vibrations, etc.) can be obtained.

Preferably, the central magnet arrangement has a first height and the two side magnet arrangements have a second height. This may provide the following advantages: the permanent magnet assembly with magnet arrangements of different heights can also be realized in a spatially (mirror) symmetrical shape.

Characteristic (C): the width of at least one of the side magnet arrangements is different, in particular larger, than the width of the central magnet arrangement.

With regard to feature (C), the inventors have found that by selecting an appropriate width, the permanent magnet assembly can be realized with a further degree of design freedom. This further degree of freedom can also be exploited in order to achieve a permanent magnet assembly that contributes to a smooth operation of the electromechanical transducer for each application.

Preferably, the central magnet arrangement has a first width and the two side magnet arrangements have a second width. This may provide the following advantages: permanent magnet assemblies with magnet arrangements of different widths can also be realized in a spatially (mirror) symmetrical shape.

According to a further aspect of the invention, a rotor assembly for an electromechanical transducer, in particular for a generator of a wind turbine, is provided. A rotor assembly is provided comprising a support structure, and at least one permanent magnet assembly as described above. The permanent magnet assembly is mounted to the support structure.

The rotor assembly provided is based on the following concept: with the PM assembly described above, a rotor assembly for an electromechanical transducer can be constructed which in operation produces efficient operation due to its magnetic focusing. In particular, unwanted effects, such as e.g. cogging torque, vibrations, etc., may be reduced, which not only results in a high efficiency factor but also in a low noise operation of the electromechanical transducer.

According to a further aspect of the invention, an electromechanical transducer, in particular a generator of a wind turbine, is provided. An electromechanical transducer is provided that includes a stator assembly and a rotor assembly as described above.

The electromechanical transducer provided is based on the following concept: with the rotor assembly described above, it is possible to design a PM electromechanical transducer in which high operational efficiency can be achieved for the at least one PM component at comparatively low manufacturing costs, since at least some unwanted effects are reduced.

According to a further aspect of the invention, a wind turbine for generating electricity is provided. The provided wind turbine comprises: a tower; a wind rotor (wind rotor) arranged at a top part of the tower and comprising at least one blade; and an electromechanical transducer as described above. The electromechanical transducer is mechanically coupled to the wind rotor.

The wind turbine provided (also named wind energy plant) is based on the following concept: the electromechanical transducer described above, representing a generator for a wind turbine, may allow for an improved efficiency of the generation of electricity and/or a reduced operational noise, while at the same time keeping the manufacturing costs of the at least one PM component small. This may help to improve the attractiveness of wind turbine technology for regenerative power generation compared to other technologies, such as solar power plants.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. Hereinafter, the present invention will be described in more detail with reference to examples of embodiments, but the present invention is not limited to these examples of embodiments.

Drawings

FIG. 1 shows a wind turbine according to an embodiment of the invention.

Fig. 2 shows a generator of the wind turbine of fig. 1 in a schematic representation.

Fig. 3 shows a Permanent Magnet (PM) assembly producing a focusing magnetic field, the PM assembly having a central magnet with an angular distribution of expansion of the domain alignment direction along respective straight lines having different orientations.

Fig. 4 shows a PM assembly with a central magnet arrangement with curved magnetic domain alignment lines.

Fig. 5 shows a two-part central magnet arrangement with straight magnetic domain alignment lines.

Fig. 6 shows a two-part central magnet device with curved magnetic domain alignment lines.

Fig. 7 shows the achievable flux density within the air gap as a function of the aspect ratio for different magnet arrangements having different widths.

Detailed Description

The illustration in the drawings is schematically. It should be noted that in different figures, similar or identical elements or features are provided with the same reference signs or with reference signs which differ from the corresponding reference signs only in the first place. In order to avoid unnecessary repetition, elements or features that have been set forth in the previously described embodiments are not set forth again at a later point in the description.

FIG. 1 shows a wind turbine 100 according to an embodiment of the invention. The wind turbine 100 includes a tower 120 mounted on a foundation, not depicted. On top of the tower 120 a nacelle 122 is arranged. Between the tower 120 and the nacelle 122 a yaw angle adjustment device 121 is provided, which is capable of rotating the nacelle 122 about a not depicted vertical axis aligned with the longitudinal extension of the tower 120. By controlling the yaw angle adjustment arrangement 121 in a suitable manner, it may be ensured that the nacelle 122 is always properly aligned with the current wind direction during normal operation of the wind turbine 100.

The wind turbine 100 further includes a rotor 110 having three blades 114. In the perspective view of fig. 1, only two vanes 114 are visible. The rotor 110 is rotatable about a rotation axis 110 a. Blades 114 mounted at hub 112 extend radially with respect to rotational axis 110 a.

Between the hub 112 and the blades 114, blade angle adjustment means 116 are respectively provided for adjusting the blade pitch angle of each blade 114 by rotating the respective blade 114 about a not depicted axis, which is aligned substantially parallel to the longitudinal extension of the respective blade 114. By controlling the blade angle adjustment means 116, the blade pitch angle of the respective blade 114 may be adjusted in such a way that the maximum wind force may be recovered (retrieve) from the available mechanical power of the wind driving the wind rotor 110, at least when the wind is not too strong.

As can be seen from fig. 1, a gearbox 124 is provided within the nacelle 122. The gearbox 124 is used to convert the number of revolutions of the rotor 110 into a higher number of revolutions of the shaft 125, which is coupled to an electromechanical transducer 140 in a known manner. The electromechanical transducer is a generator 140.

At this point it should be noted that the gearbox 124 is optional and that the generator 140 may also be coupled directly to the rotor 110 via the shaft 125 without changing the number of revolutions. In this case, the wind turbine is a so-called Direct Drive (DD) wind turbine.

Further, a brake 126 is provided in order to stop the operation of the wind turbine 100, for example in case of an emergency or in order to reduce the rotational speed of the rotor 110.

The wind turbine 100 further comprises a control system 153 for operating the wind turbine 100 in an efficient manner. In addition to controlling, for example, the yaw angle adjustment device 121, the depicted control system 153 is also used for adjusting the blade pitch angle of the rotor blades 114 in an optimized manner.

According to the basic principles of electrical engineering, the generator 140 includes a stator assembly 145 and a rotor assembly 150. In the embodiment described herein, the generator 140 is implemented in a so-called "inner stator-outer rotor" configuration, wherein the rotor assembly 150 surrounds the stator assembly 145. This means that the non-depicted permanent magnet arrangement of the rotor assembly 150, respectively the magnet assembly, travels around an arrangement of a plurality of non-depicted coils of the inner stator assembly 145, which coils generate induced currents resulting from the time varying magnetic flux obtained from the traveling permanent magnet arrangement.

According to embodiments described herein, each Permanent Magnet (PM) assembly includes at least three sintered permanent magnet arrangements made from a Nd-Fe-B material composition.

Fig. 2 shows a schematic representation of the generator 140 in a cross-sectional view. The generator 140 includes a stator assembly 145. The stator assembly 145 includes: a stator support structure 247 comprising a stack of a plurality of laminations; and a plurality of stator windings 249 housed within the stator support structure 247. The windings 249 are interconnected in a known manner by means of electrical connections not depicted.

The rotor assembly 150 of the generator 140, which is separated from the stator assembly 145 by an air gap ag, includes a rotor support structure 252 that provides a mechanical foundation for mounting a plurality of Permanent Magnet (PM) assemblies 260, each PM assembly including three magnet devices: a center magnet assembly 270, a first side magnet assembly 280a, and a second side magnet assembly 280 b. The central magnet assembly 270 is positioned between or sandwiched between two

side magnet assemblies

280a, 280 b. The main surface of the central magnet assembly 270 is designated by reference numeral 270 a.

It should be noted that in fig. 2, only one PM component 260 is depicted for ease of illustration. In practice, depending on the size of the generator 140, a plurality of PM assemblies 260 are mounted to the rotor support structure 252. The PM assemblies 260 are preferably arranged in a matrix-like configuration about the curved surface area of the support structure 252 having a substantially cylindrical geometry about the generator axis 240 a.

As can be seen from fig. 2, the PM assembly 260 is not directly mounted to the rotor support structure 252. Instead, for each PM assembly 260, a back plate 254 made of a ferromagnetic material (e.g., iron) is provided. The back plate 254 is provided to ensure proper guidance of the magnetic flux. This significantly reduces the strength of the stray magnetic field in a beneficial way.

Fig. 3 illustrates a Permanent Magnet (PM) assembly 360 according to an embodiment of the invention. The PM assembly 360 includes three magnet arrangements, which are also shown in fig. 2 and already mentioned above.

Magnet assemblies

280a, 270 and 280b are mounted to back plate 254.

As can be seen from fig. 3, the central magnet piece 270 is magnetized in such a way that an angular distribution of the expansion of the domain alignment directions 375, each following a straight magnetization line 375a, is given. The lines 375a are angled or slanted relative to each other in a fan-like manner. In particular, the spread angle distribution of the straight magnetization lines 375a produces a focal point 377 in a region above the main surface 270a, which is characterized by a local maximum of the magnetic field, respectively the magnetic flux density.

According to the exemplary embodiments described herein, the magnetic domain alignment pattern is symmetric about the axis of symmetry 377 a. In this document, the axis of symmetry 377a is also named magnetic axis. The magnetic axis 377a is a normal axis to the major surface 270 and extends through the focal point 377.

The two

side magnet arrangements

280a, 280b each have only a single magnetic domain alignment direction resulting in unfocused magnetization. In this embodiment, the constant angle between the alignment direction and the magnetic axis 377a

(θ) is approximately 40 °. Since the magnetization of the two

side magnet arrangements

280a, 280b should support the magnetic field strength, respectively the magnetic flux density, in the region of the focal point 377, the angle is such that

(θ) may vary depending on the magnetic focal length (i.e., the distance between the focal point 377 and the major surface 270 a).

Fig. 4 shows a PM assembly 460 with a central magnet arrangement 470 having an angular spread of the domain alignment direction 475. As can be seen from this figure, the corresponding magnetic domain alignment pattern has a curved magnetic domain alignment line 475 a. All lines 475a "leave" the central magnet assembly 470 at the main surface 470a in such a way that at least a certain degree of magnetic focusing is achieved. The magnetic symmetry axis is designated with reference numeral 477 a.

As can be further seen from fig. 4, in this "symmetric" embodiment, half of the magnetic domain alignment line 475a "enters" the central magnet device 470 from the right lateral surface thereof or from the right portion of the bottom surface opposite the main surface 470 a. Along this direction, these lines 475a are bent rightward.

Correspondingly, the other half of the magnetic domain alignment line 475a "enters" the central magnet device 470 from the left lateral surface thereof or from the left portion of the bottom surface opposite the main surface 470 a. Along this direction, these other lines 475a are bent leftward.

It should be noted that the terms "exit" and "entry" are arbitrary in that they refer to the magnet direction from south to north. When the opposite magnet orientation is assumed, all lines 475a "enter" the central magnet assembly 470 via the main surface 470 a.

Fig. 5 shows a two-part central magnet arrangement 570 with straight magnetic domain alignment lines. The central magnet assembly 570 is comprised of two magnet pieces: a first magnet piece 571 and a second magnet piece 572.

In fig. 5, the two

magnet pieces

571, 572 are depicted spaced apart from each other with a small gap between them for illustration purposes only. In order to form a focusing magnet arrangement which produces as undisturbed a magnetic field as possible, it is generally preferred that the

magnet pieces

571, 572 are arranged without a gap between them.

The assembly or assembly of the central magnet arrangement 570 from two relatively small magnet pieces 571, 752 provides the following advantages: it is not necessary to manufacture (sintered) single magnets with a complete angular distribution of the expansion leading to the alignment direction of the domains of the focused magnetization. It is quite sufficient to manufacture only a smaller magnet piece having only a portion (e.g., half) of the complete focused domain alignment pattern. The manufacturing effort for a larger number of smaller focusing magnet arrangements may be significantly smaller than the manufacturing effort for a smaller number of larger focusing magnet arrangements. Thus, in many applications it may be advantageous to assemble the central focusing magnet arrangement by means of two or more single focusing magnet pieces.

Of course, it should be mentioned that the central magnet arrangement 570 may also consist of three or more magnet pieces.

Fig. 6 shows a two-part central magnet assembly 670 with curved magnetic domain alignment lines. The central magnet assembly 670 is comprised of two magnet pieces: a first magnet piece 671 and a second magnet piece 672. With respect to manufacturing efforts, the same considerations and advantages as described above for the central magnet arrangement 570 apply.

Also, the central magnet assembly 670 may be comprised of three or more different magnet pieces.

Fig. 7 shows a graph in which the magnetic flux density within the air gap of the generator (which may be produced with different magnet arrangements) is plotted as a function of the aspect ratio of the respective magnet arrangement. In this context of a focusing magnet arrangement, the aspect ratio is the ratio between the height and the width of the magnet arrangement, wherein the height is measured in a direction parallel to the magnetic axis and the width is given by the dimension of the magnet arrangement in a direction perpendicular to the height direction. For a magnet assembly having two parallel magnetized side magnet arrangements sandwiching a focused central magnet arrangement, the width is the distance between the mutually facing side surfaces of the two side magnet arrangements.

In the graph of fig. 7, the curve pointed at 780 depicts, for comparison purposes, an air gap flux density that can be achieved with a parallel magnetized magnet arrangement having a width of 50 mm. Curve 782 depicts the corresponding air gap flux density that can be achieved with a focusing magnet arrangement having the same spatial dimensions. As can be seen from the comparison between the two

curves

780 and 782, for larger aspect ratios, the difference between the larger flux density produced by the focusing magnet arrangement and the smaller flux density produced by the parallel magnetized magnet arrangement is greater. As the aspect ratio increases, curve 782 shows a significant increase starting from 0.2 and going all the way to 0.6. For aspect ratios greater than 0.8, the achievable air gap flux density increases only to a much smaller extent.

Curves

784 and 786 show corresponding curves for a magnet arrangement having a width of 100 mm. Again, the difference between the larger magnetic flux density produced by the focusing magnet arrangement (see curve 786) and the smaller magnetic flux density produced by the parallel magnetized magnet arrangement (see curve 784) becomes larger as the aspect ratio increases. For a 100 mm magnet arrangement, saturation is achieved for aspect ratios greater than 0.4.

It is not surprising that for larger magnet arrangements (here for magnet arrangements with a width of 100 mm) the absolute value of the magnetic flux density that can be achieved in the air gap is significantly larger.

From the considerations presented above, it can be seen that the aspect ratio is an additional parameter that can be varied in order to increase the air gap flux density. Of course, the degree of flux focusing can also be controlled by altering the position of the focal region.

It should be noted that the term "comprising" does not exclude other elements or steps and the use of "a" or "an" does not exclude a plurality. Also, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A permanent magnet assembly (360, 460), comprising:

a central magnet arrangement (270, 470);

a first side magnet arrangement (280 a) arranged at a first side of the central magnet arrangement (270, 470); and

a second side magnet arrangement (280 b) arranged at a second side of the central magnet arrangement (270, 470); wherein

-the central magnet arrangement (270, 470) is sandwiched between the first side magnet arrangement (280 a) and the second side magnet arrangement (280 b),

-said central magnet arrangement (270, 470) having an angular spread of domain alignment directions (375, 475) resulting in a focusing magnetization, said focusing magnetization defining a focal point (377),

-both the first side magnet arrangement (280 a) and the second side magnet arrangement (280 b) have only single magnetic domain alignment directions (382 a, 382 b) resulting in parallel magnetization, and

-the single magnetic domain alignment direction (382 a, 382 b) is inclined with respect to a magnetic axis (377 a) defined by a shortest distance between the focal point (377) and a main surface (270 a) of the central magnet arrangement (270, 470).

2. The permanent magnet assembly (360, 460) according to the preceding claim, wherein

The magnetic axis (377 a) is an axis of symmetry of the central magnet arrangement (270, 470), wherein symmetry is given by the spatial shape and size of the central magnet arrangement (270, 470) and/or by the angular spread distribution of the magnetic domain alignment direction (375, 475).

3. The permanent magnet assembly (360, 460) according to the preceding claim, wherein

The magnetic axis (377 a) is an axis of symmetry of the entire permanent magnet assembly (360, 460), wherein symmetry is given by the spatial shape and size of the entire permanent magnet assembly (360, 460) and/or by the overall distribution of magnetic domain alignment directions (375, 382a, 382 b).

4. The permanent magnet assembly (360, 460) according to any of the preceding claims 1 to 3, wherein

At least one of the central magnet arrangement (270, 470), the first side magnet arrangement (280 a), and the second side magnet arrangement (280 b) is formed as a single magnet piece.

5. The permanent magnet assembly according to any of the preceding claims 1 to 3, wherein

At least one of the central magnet arrangement (570, 670), the first side magnet arrangement and the second side magnet arrangement comprises at least two magnet pieces (571, 572, 671, 672).

6. Permanent magnet assembly according to the preceding claim, wherein

The two magnet pieces (571, 572, 671, 672) directly abut against one another.

7. The permanent magnet assembly (360, 460) according to any of the preceding claims, wherein

At least one of the central magnet arrangement (570, 670), the first side magnet arrangement (280 a) and the second side magnet arrangement (280 b) is a sintered magnet, in particular a sintered magnet comprising NdFeB.

8. The permanent magnet assembly (360) according to any of the preceding claims 1 to 7, wherein

The angular distribution of expansion of the magnetic domain alignment direction (375) includes a straight line (375 a).

9. The permanent magnet assembly (460) according to any of the preceding claims 1 to 7, wherein

The expanded angular distribution of magnetic domain alignment directions (475) includes curved magnetic domain alignment lines (475 a).

10. The permanent magnet assembly (460) according to the preceding claim, wherein

For the central magnet arrangement (470),

(i) a first angle between the magnetic domain alignment direction (475) and (ii) a magnetic axis (477 a) at the major surface (470 a) is less than a second angle between (i) the magnetic domain alignment direction (475) and (ii) the magnetic axis (477 a) at an interface between the central magnet device (470) and at least one of the two side magnet devices (280 a, 280 b).

11. The permanent magnet assembly (360, 460) according to any of the preceding claims, wherein

For at least one of the first side magnet arrangement (280 a) and the second side magnet arrangement (280 b),

a tilt angle between the single magnetic domain alignment direction (382 a, 382 b) and the magnetic axis (377 a) ((

) In the range of 20 ° and 70 °, preferably in the range of 30 ° and 60 °, and more preferably in the range of 40 ° and 50 °.

12. The permanent magnet assembly (360, 460) according to any of the preceding claims, wherein

Each of the magnet arrangements comprises a height and a width, wherein the height is measured in a direction parallel to the magnetic axis (377 a) and the width is measured in a direction parallel to a common normal vector of mutually facing side surfaces of the two side magnet arrangements (280 a, 280 b), wherein the magnet assembly comprises at least one of the following features:

(A) the central magnet arrangement (270, 470) comprises an aspect ratio in the range between 0.2 and 1.0, particularly between 0.4 and 1.0, and more particularly between 0.6 and 1.0, wherein the aspect ratio is defined by the ratio between the height and the width of the central magnet arrangement (270, 470);

(B) the height of the central magnet arrangement is different, in particular greater, than the height of at least one of the side magnet arrangements; and

(C) the width of at least one of the side magnet arrangements is different, in particular larger, than the width of the central magnet arrangement.

13. A rotor assembly (150) for an electromechanical transducer (140), in particular a generator (140) for a wind turbine (100), the rotor assembly (150) comprising:

a support structure (252), and

the at least one permanent magnet assembly (260, 360, 460) according to any one of the preceding claims, wherein the permanent magnet assembly (260, 360, 460) is mounted to the support structure (252).

14. An electromechanical transducer (140), in particular a generator (140) of a wind turbine (100), the electromechanical transducer (140) comprising:

a stator assembly (145), and

the rotor assembly (150) according to the preceding claim.

15. A wind turbine (100) for generating electricity, the wind turbine (100) comprising:

a tower (120) having a plurality of towers,

a wind rotor (110) arranged at a top portion of the tower (120) and comprising at least one blade (114), and

the electromechanical transducer (140) according to the preceding claim, wherein the electromechanical transducer (140) is mechanically coupled with the wind rotor (110).