Permanent magnet rotors for electrical machines

Abstract

The present disclosure relates to permanent magnet rotors for an electrical machine. The permanent magnet rotors comprise a rotor rim, comprising a circumferential surface with at least a first rib and a second rib extending along an axial direction, and a plurality of permanent magnet modules mounted on the rotor rim surface extending along an axial direction, each of the modules comprising a module base supporting one or more permanent magnets. The module base comprises a first lateral surface and a second lateral surface. Further, a shape of the first and second lateral surfaces is substantially complementary to a shape of the first and second ribs such that the first and second ribs at least partially support the first and second lateral surfaces of the module base. The present disclosure also relates to wind turbines generators comprising the permanent magnet rotors.

Description

PERMANENT MAGNET ROTORS FOR ELECTRICAL MACHINESFIELD

[0001] The present disclosure relates to a rotor for an electrical machine, and more particularly relates to a permanent magnet rotor for a wind turbine generator. The present disclosure further relates to permanent magnet modules for a permanent magnet rotor of an electrical machine, e.g. a wind turbine generator.BACKGROUND

[0002] Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly ("directly driven" or "gearless") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

[0003] Wind turbine generators, and other electrical machines such as motors, generally comprise a rotor and a stator. The rotor rotates with respect to the stator. The rotor may be the inner structure and the stator the other structure. The stator therefore may radially surround the rotor. Alternatively, in other configurations the arrangement may be opposite, with the rotor radially surrounding the stator.

[0004] Large electrical generators, such as those used in modern wind turbines (particularly direct drive wind turbines), may be permanent magnet excited generators (PMG) or electrically excited generators.

[0005] Electrically excited generators generally comprise a rotor having a plurality of pole shoes and excitation windings, i.e., coils. In use, a current is applied to the excitation coils. The applied current creates the polarity of the poles, wherein adjacent poles have a different magnetic polarity. As the rotor turns, the magnetic field from the pole shoes is applied to the windings of the stator causing a variable magnetic flux in the stator windings and producing a voltage in the stator windings. Thus, in electrically excited generators, the magnetic field togenerate the electrical power is created electrically, and therefore permanent magnets are not required.

[0006] In the case of permanent magnet generators (PMG), permanent magnets (PM) are generally arranged on the rotor, whereas winding elements i.e. coils are usually included in the stator. Alternatively, permanent magnets could also be arranged in the stator structure and winding elements in the rotor structure. Permanent magnet generators are generally deemed to be reliable and require less maintenance than other generator typologies. The prospect of less maintenance makes permanent magnet generators an attractive option specifically for offshore wind turbines. In addition, the torque density of permanent magnet generators allows to have a more compact and relatively lightweight generator.

[0007] Permanent magnets may be provided in permanent magnet modules, which may carry multiple magnets but be attached to the rotor as a single item. A permanent magnet module may be defined as a unit having a plurality of permanent magnets, such that the plurality of magnets can be mounted to and unmounted together from a rotor of an electrical machine. Such a module may have a module base with a shape suitable for housing or carrying a plurality of permanent magnets that may be fixed to the base. The base may be configured to be fixed to a rotor rim in such a way that the plurality of magnets are fixed together to the rotor rim through the module base.

[0008] The use of permanent magnet modules may thus facilitate the manufacturing of a rotor. The use of permanent magnet modules may also facilitate maintenance of the rotor: in case of a problem with a magnet, the magnet module may be removed and replaced by a new module.

[0009] Permanent magnet modules may have a module base formed as a stack of metal sheets separated from each other by means of electrically insulating material. With this feature, magnetic losses, for example eddy currents, might be reduced in the corresponding electrical machine such that its efficiency may be improved.

[0010] Permanent magnets of direct drive offshore wind turbines are generally arranged on the permanent magnet module in a flat configuration or in V-shape configuration. However, these magnet configurations are not limited to generators in direct drive offshore applications and not even to the field of wind turbines only. Generators of considerable dimensions that may have similar configurations may also be found e.g. in steam turbines, water turbines and marine propulsion motors.

[0011] In a flat configuration, the permanent magnets may be mounted substantially parallel with respect to a (local) radial direction, i.e. the direction extending radially from the center of the rotor to the module, on a flat or tangential surface of the base. Magnets aregenerally glued to the base and may be additionally covered by a plate to improve the fixation to the base. All the magnets within a module typically have the same magnetic orientation, i.e. the North of all the magnets face towards the stator, and the magnetic orientation of the neighboring module is the opposite, as to have a radial magnetic configuration. Compared to other configurations, in flat or tangential configurations the area of the permanent magnets is generally bigger. However, permanent magnets may be occasionally detached from the base due to adhesive failure, especially in applications having a long-life expectancy or working in a corrosive atmosphere as for example in wind turbines, in particular in offshore wind turbines.

[0012] In magnet modules having a V-shape configuration, the magnet modules are arranged inclined with respect to the (local) radial direction, i.e. the direction extending radially from the center of the rotor to (and through) a center of the module. In these configurations, magnets may be embedded in the base or clamped between the base and a central support fixed to the base. In these configurations, the permanent magnets may have a circumferential magnetic orientation (also sometimes referred to as "transversal" or "tangential" flux orientation). Magnetic fields and operation may be more efficient in V-shape configurations since the magnetic flux is more concentrated. However, such configurations generally require more space and may thus have a lower utilization of the module.

[0013] V-shape as used throughout the present disclosure may be regarded as any shape of magnets resembling a shape of the letter V, or of the letter V when inverted. A V-shape implies that the permanent magnets form at least two legs, which are inclined with respect to each other, i.e. they are closer to each other on one end, and further away from each other at an opposite end of the magnets. The two legs of the permanent magnets in a permanent magnet module may be closer to each other at a side close to the base of a permanent magnet module, or instead may be closer at a side close to an airgap of an electrical machine.

[0014] A permanent magnet module may include a horizontal portion in between the two inclined legs. This is still to be considered as covered by the word V-shape.

[0015] A V-shape as used throughout the present disclosure should also be understood to cover magnet arrangements covering more than a single “V”. For example, permanent magnet modules including permanent magnets arranged in a W-shape, i.e. two “V”’s next to each other should also be considered to be covered.

[0016] As previously mentioned, the permanent magnet module base may generally be fixed to the rotor rim, which is made of steel or cast iron. Rotor rims of large electric machines e.g. direct-drive wind turbine generators, comprise features which aim to give additional stiffness to the supporting structure, such that deformation of the rotor is avoided or reduced and the lifecycle of the rotor is extended. However, these features increase the size and thecost of the machine while adding additional weight.

[0017] The present disclosure provides systems and methods to at least partially overcome some of the aforementioned drawbacks.SUMMARY

[0018] In an aspect of the present disclosure, a permanent magnet rotor for an electrical machine is provided. The permanent magnet rotor comprises a rotor rim, comprising a circumferential surface with at least a first rib and a second rib extending along an axial direction. The permanent magnet rotor also comprises a plurality of permanent magnet modules mounted on the rotor rim surface extending along an axial direction, the modules comprising a module base supporting one or more permanent magnets. The module base comprises a first lateral surface and a second lateral surface. A shape of the first and second lateral surfaces is substantially complementary to a shape of the first and second ribs such that the first and second ribs at least partially support the first and second lateral surface of the module base.

[0019] According to this aspect, deformation of the permanent magnet rotor may be avoided or reduced while providing a permanent magnet rotor with reduced size and weight. The ribs contribute to keeping the magnet module in position, providing support and protecting the module from the tangential forces. The ribs provide structural support, contributing to global stiffness of the rotor. Air gap stability may be increased.

[0020] External reinforcement of the rotor may not be needed, leading to a more compact rotor design with less weight. Further, the base of the magnet module may comprise less electrical steel, which is replaced by rim material, which may be more cost effective.

[0021] Throughout the present disclosure, an axial direction may be defined as a direction coinciding with the rotational axis of the rotor or parallel thereto. An axial cross-section may be defined as the cross-section with a plane that is perpendicular to the rotational axis of the rotor.

[0022] Throughout the present disclosure, ribs of the rotor rim may be regarded as structural or supporting members of the rotor rim which provide stiffness.

[0023] In another aspect of the present disclosure, a permanent magnet module for an electrical machine is provided. The permanent magnet module comprises one or more permanent magnets and a module base configured to be attached to a rotor rim and support the one or more permanent magnets, and comprising a first lateral surface and a secondlateral surface. The first and second lateral surfaces of the module base are curved or inclined and extend in a radial direction towards an air gap and outwardly away from each other.

[0024] In a further aspect of the present disclosure, a rotor for a permanent magnet rotor of an electrical machine is provided. The rotor comprises a rotor rim having an active part surface facing an air gap of the electrical machine. The rotor further comprises a plurality of ribs at the active part of the surface extending along an axial direction. The ribs are configured to receive a module base of permanent magnet module between them.

[0025] Additional objects, advantages and features of embodiments of the present disclosure will become apparent to those skilled in the art upon examination of the description, or may be learned by practice.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 schematically illustrates a perspective view of one example of a wind turbine;

[0027] Figure 2 illustrates an example of a hub and a nacelle of a wind turbine;

[0028] Figure 3 schematically illustrates an axial cross-section of a permanent magnet rotor according to an example of the present disclosure;

[0029] Figure 4 schematically illustrates an axial cross-section of a permanent magnet rotor according to another example of the present disclosure;

[0030] Figure 5 schematically illustrates an axial cross-section of a permanent magnet rotor according to a further example of the present disclosure; and

[0031] Figure 6 schematically illustrates an axial cross-section of a permanent magnet rotor according to another example of the present disclosure.DETAILED DESCRIPTION OF EXAMPLES

[0032] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the teaching. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0033] Figure 1 is a perspective view of an example of a wind turbine 10. In the example, the wind turbine 10 is a horizontal-axis wind turbine. Alternatively, the wind turbine 10 may be a vertical-axis wind turbine. In the example, the wind turbine 10 includes a tower 15 that extends from a support system 14 on a ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 that is coupled to nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from the hub 20. In the example, the rotor 18 has three rotor blades 22. In an alternative embodiment, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in figure 1) between a support system 14 and the nacelle 16. In an alternative embodiment, the tower 15 is any suitable type of a tower having any suitable height. According to an alternative, the tower can be a hybrid tower comprising a portion made of concrete and a tubular steel portion. Also, the tower can be a partial or full lattice tower.

[0034] The rotor blades 22 are spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. The rotor blades 22 are mated to the hub 20 by coupling a blade root portion 24 to the hub 20 at a plurality of load transfer regions 26. The load transfer regions 26 may have a hub load transfer region and a blade load transfer region (both not shown in figure 1). Loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0035] In examples, the rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 m or more. Rotor blades 22 may have any suitable length that enables the wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include 20 m or less, 37 m, 48.7 m, 50.2m, 52.2 m or a length that is greater than 91 m. As wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 is rotated about a rotor axis 30. As the rotor blades 22 are rotated and subjected to centrifugal forces, the rotor blades 22 are also subjected to various forces and moments. As such, the rotor blades 22 may deflect and / or rotate from a neutral, or non-deflected, position to a deflected position.

[0036] Moreover, a pitch angle of the rotor blades 22, i.e., an angle that determines an orientation of the rotor blades 22 with respect to the wind direction, may be changed by a pitch system 32 to control the load and power generated by the wind turbine 10 by adjusting an angular position of at least one rotor blade 22 relative to wind vectors. Pitch axes 34 of rotor blades 22 are shown. During operation of the wind turbine 10, the pitch system 32 may particularly change a pitch angle of the rotor blades 22 such that the angle of attack of (portions of) the rotor blades are reduced, which facilitates reducing a rotational speed and / or facilitates a stall of the rotor 18.

[0037] In the example, a blade pitch of each rotor blade 22 is controlled individually by a wind turbine controller 36 or by a pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by said control systems.

[0038] Further, in the example, as the wind direction 28 changes, a nacelle 16 may be rotated about a yaw axis 38 to position the rotor blades 22 with respect to wind direction 28.

[0039] In the example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed system throughout the wind turbine 10, on the support system 14, within a wind farm, and / or at a remote-control center. The wind turbine controller 36 includes a processor 40 configured to perform the methods and / or steps described herein. Further, many of the other components described herein include a processor.

[0040] As used herein, the term "processor” is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific, integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and / or a control system can also include memory, input channels, and / or output channels.

[0041] Figure 2 is an enlarged sectional view of a portion of the wind turbine 10. In the example, the wind turbine 10 includes the nacelle 16 and the rotor 18 that is rotatably coupled to the nacelle 16. More specifically, the hub 20 of the rotor 18 is rotatably coupled to an electric generator 42 positioned within the nacelle 16 by the main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In the example, the main shaft 44 is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle 16. A rotation of the main shaft 44 drives the gearbox 46 that subsequently drives the high-speed shaft 48 by translating the relatively slow rotational movement of the rotor 18 and of the main shaft 44 into a relatively fast rotational movement of the high-speed shaft 48. The latter is connected to the generator 42 for generating electrical energy with the help of a coupling 50. Furthermore, a transformer 90 and / or suitable electronics, switches, and / or inverters may be arranged in the nacelle 16 in order to transform electrical energy generated by the generator 42 having a voltage between 400V to 1000 V into electrical energy having medium voltage, e.g. 10 - 35 KV. Said electrical energy is conducted via power cables from the nacelle 16 into the tower 15.

[0042] The gearbox 46, generator 42 and transformer 90 may be supported by a main support structure frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing that is connected to the main frame 52 by one or more torque arms 103. In the example, the nacelle 16 also includes a main forward supportbearing 60 and a main aft support bearing 62. Furthermore, the generator 42 can be mounted to the main frame 52 by decoupling support means 54, in particular in order to prevent vibrations of the generator 42 to be introduced into the main frame 52 and thereby causing a noise emission source.

[0043] Optionally, the main frame 52 is configured to carry the entire load caused by the weight of the rotor 18 and components of the nacelle 16 and by the wind and rotational loads, and furthermore, to introduce these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and any associated fastening, support, and / or securing device including, but not limited to, main frame 52, and forward support bearing 60 and aft support bearing 62, are sometimes referred to as a drive train 64.

[0044] In some examples, the wind turbine may be a direct drive wind turbine without gearbox 46. Generator 42 operate at the same rotational speed as the rotor 18 in direct drive wind turbines. They therefore generally have a much larger diameter than generators used in wind turbines having a gearbox 46 for providing a similar amount of power than a wind turbine with a gearbox.

[0045] The nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 and thereby also the rotor 18 about the yaw axis 38 to control the perspective of the rotor blades 22 with respect to the wind direction 28.

[0046] For positioning the nacelle 16 appropriately with respect to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system 58 which may include a wind vane and anemometer. The meteorological measurement system 58 can provide information to the wind turbine controller 36 that may include wind direction 28 and / or wind speed. In the example, the pitch system 32 is at least partially arranged as a pitch assembly 66 in the hub 20. The pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in figure 1) for modulating the pitch angle of a rotor blade 22 along the pitch axis 34. Only one of three pitch drive systems 68 is shown in figure 2.

[0047] In the example, the pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and to a respective rotor blade 22 (shown in figure 1) for rotating the respective rotor blade 22 about the pitch axis 34. The pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. The pitch drive motor 74 is coupled to the pitch drive gearbox 76 such that the pitch drive motor 74 imparts mechanical force to the pitch drive gearbox 76. The pitch drive gearbox 76 is coupled to the pitch drive pinion 78 such that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. The pitchbearing 72 is coupled to pitch drive pinion 78 such that the rotation of the pitch drive pinion 78 causes a rotation of the pitch bearing 72.

[0048] Pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of a rotor blade 22 upon receipt of one or more signals from the wind turbine controller 36. In the example, the pitch drive motor 74 is any suitable motor driven by electrical power and / or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components such as, but not limited to, hydraulic cylinders, springs, and / or servomechanisms. In certain embodiments, the pitch drive motor 74 is driven by energy extracted from a rotational inertia of hub 20 and / or a stored energy source (not shown) that supplies energy to components of the wind turbine 10.

[0049] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive system 68 according to control signals from the wind turbine controller 36, in case of specific prioritized situations and / or during rotor 18 overspeed. In the example, the pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a respective pitch drive system 68 for controlling pitch drive system 68 independently from the wind turbine controller 36. In the example, the pitch control system 80 is coupled to the pitch drive system 68 and to a sensor 70. During normal operation of the wind turbine 10, the wind turbine controller 36 may control the pitch drive system 68 to adjust a pitch angle of rotor blades 22.

[0050] According to an embodiment, a power generator 84, for example comprising a battery and electric capacitors, is arranged at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and to the pitch drive system 68 to provide a source of power to these components. In the example, the power generator 84 provides a continuing source of power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, power generator 84 provides power to the pitch assembly 66 only during an electrical power loss event of the wind turbine 10. The electrical power loss event may include power grid loss or dip, malfunctioning of an electrical system of the wind turbine 10, and / or failure of the wind turbine controller 36. During the electrical power loss event, the power generator 84 operates to provide electrical power to the pitch assembly 66 such that pitch assembly 66 can operate during the electrical power loss event.

[0051] In the example, the pitch drive system 68, the sensor 70, the pitch control system 80, cables, and the power generator 84 are each positioned in a cavity 86 defined by an inner surface 88 of hub 20. In an alternative embodiment, said components are positioned withrespect to an outer roof surface of hub 20 and may be coupled, directly or indirectly, to the outer roof surface.

[0052] Figure 3 schematically illustrates an axial cross-section of a permanent magnet rotor 100 for an electrical machine according to an example of the present disclosure.

[0053] The permanent magnet rotor 100 comprises a rotor rim 200 comprising a circumferential surface with at least a first rib 210 and a second rib 220 extending along an axial direction. The permanent magnet rotor 100 also comprises a plurality of permanent magnet modules 300 mounted on the rotor rim surface and extending along an axial direction. Each of the modules comprises a module base 310 supporting one or more permanent magnets 320.

[0054] The module base 310 comprises a first lateral surface 312 and a second lateral surface 313. A shape of the first and second lateral surfaces 312, 313 is substantially complementary to a shape of the first and second ribs such that the first and second ribs 210, 220 at least partially support the first and second lateral surfaces 312, 313 of the module base.

[0055] A permanent magnet rotor with reduced weight and improved global stiffness may be provided. Deformation of the rotor may be prevented and a global stability of the air gap may be enhanced. The ribs are used as path for the magnetic circuit as they are located at least partially in the magnetic circuit path. They provide high permeability for the magnetic field and they also contribute to keeping the permanent magnet module in position, acting as an anchoring point for the active parts. Weight reduction may be achieved by integrating the active parts and the stiffening structures of the permanent magnet rotor. The ribs are configured to support a module base of the permanent magnet module.

[0056] In particular, the example of figure 3 shows a rotor rim 200 having an active part surface facing an air gap of the electrical machine. The rotor rim comprises a plurality of ribs at the active surface extending along an axial direction.

[0057] The ribs 210, 220 or stiffener ribs may be protrusions of the rotor rim 200 extending in an axial direction of the rotor rim. The ribs 210, 220 may be made of the same material as the rotor rim, in particular the ribs may be integrally formed with the rotor rim. In some examples, the ribs may be made of solid iron. In other examples, the ribs may be made of solid steel. The term “solid” may be regarded as non-laminated i.e. steel or iron which are integrally formed.

[0058] The ribs may allow the reduction of laminated material from the permanent magnet module base, reducing its cost of production and enhancing the overall stiffness of the rotor. Further, reducing the amount of magnetic material present in the module base may allowreduction of the energy required to magnetize the magnets after they have been assembled in the module The flux lines may be easier to orientate and the magnetizing energy needed may be potentially lower than in other prior art solutions.

[0059] The ribs may taper outwardly in a radial direction towards an air gap. The first rib 210 and the second rib 220 may define a space between them, such that a permanent magnet module 300 may be mounted between the first and second ribs 210, 220. A shape of the first and second lateral surfaces 312, 313 of the permanent magnet module base 310 is substantially complementary to a shape of the first and second ribs 210, 220.

[0060] The first rib 210 and the second rib 220 may have a first side and a second side. The first lateral surface 312 of the module base may contact the first side of the rib. Adjacent sides of the first and second ribs 210, 220 may define a mounting area of the permanent magnet module 300. The ribs may be part of the magnetic circuit.

[0061] As shown in figure 3, the ribs 210, 220 may substantially have a triangular crosssection. The first and second sides of adjacent ribs may contact the permanent magnet module 300. The first and second ribs 210, 220 support the first and second lateral surfaces 312, 313 of the module base 310, allowing the ribs to provide structural support to the rotor.

[0062] The ribs 210, 220 may securely fix the module base 310 to the rotor rim 200. The magnet module 320 may be easily mounted to the rotor rim, as the ribs may help identify where they should be assembled, and as the module base may match the area left between two ribs.

[0063] In some examples, the ribs 210, 220 may be integrally formed with the rotor rim 200 circumferential surface. The rotor rim may thus be manufactured such that the ribs form part of its surface, e.g. a cutting tool may be used to shape or mill the surface of the rotor rim such that it comprises ribs or protrusions defining a space configured to support a permanent magnet module.

[0064] Figure 3 further shows a permanent magnet module 300 for an electrical machine mounted on the surface of a rotor rim 200. The permanent magnet module 300 is supported between first and second ribs 210, 220 of the rotor rim.

[0065] The permanent magnet module 300 extends along an axial direction and comprises a module base 310 supporting one or more permanent magnets 320. The module base 310 comprises a first lateral surface 312 and a second lateral surface 313. The module base may further comprise a bottom surface 311, as shown in the example of figure 3. The shape of the first and second lateral surfaces 312, 313 is substantially complementary to a shape of the first and second ribs 210, 220. Further, the first and second lateral surfaces ofthe module base are curved or inclined and extend in a radial direction towards an air gap and outwardly away from each other.

[0066] During normal operation, the permanent magnet module 300, fixed to the rotor rim 200, may be under radial force due to attraction to the stator pole shoes. In addition, the permanent magnet module may be subjected to tangential forces which may lead to sliding. The stiffener ribs may provide an overall structural support to the permanent magnet rotor and may prevent the permanent magnet modules to move in a tangential direction.

[0067] In some examples, the module base 310 may be made from steel or another high magnetic permeability material. The module base 310 may be made of steel laminations. Steel laminations may minimize power and energy loss e.g. hysteresis loss or Eddy currents. In some examples, the module base may substantially have a V-shaped cross-section.

[0068] The permanent magnet module 300 may be mechanically attached to the rotor rim 200 e.g. using bolts 400 extending radially. In some examples, the number of the bolts and / or the metrics of the bolts used to mechanically attach the permanent magnet module to the rotor rim may be reduced thanks to the support provided by the ribs.

[0069] In the example shown in figure 3, the permanent magnet module 300 comprises three permanent magnets arranged in a V-shaped configuration. In other examples, other configurations of the permanent magnets are possible e.g. flat configuration of the magnets. In other examples, the permanent magnet module 300 comprises a single permanent magnet. The rotor ribs may adapt to the configuration of the permanent magnet.

[0070] The one or more permanent magnets 320 may be made e.g. from AINiCo steel (Aluminium-Nickel-Cobalt), rare earth magnetic materials such as neodymium (NdFeB) or samarium-cobalt, but may also be made from e.g. ceramic materials.

[0071] The permanent magnet module 300 may comprise a central magnet support 330 which may act as a flux concentrator comprising a substantially triangular cross-section. The permanent magnets 320 may be located between the central magnet support 330 and the module base 310. The central magnet support 330 may comprise a surface delimiting the airgap 335. Further, the central magnet support 330 may comprise an axial hole in which a rod may be inserted. The permanent magnet 300 may be fixed to the rotor rim 200 with radial bolts 400 engaging the rod in the axial hole. In other examples, not illustrated, an upper part of the central magnet support 330 may contact an upper part of the first and second ribs 210, 220. The upper part of the first and second ribs 210, 220 may therefore support the central magnet support 330 of the permanent magnet module 300, providing further structural support to the rotor.

[0072] Figure 4 shows another example of a permanent magnet rotor for an electrical machine according to the present disclosure. As previously described with reference to figure 3, the permanent magnet rotor comprises a rotor rim and a plurality of permanent magnet modules mounted on the rotor rim surface.

[0073] In the example of figure 4, the ribs 210, 220 may be mechanically attached to the rotor rim 200 surface e.g. using a plurality of bolts extending radially. In these examples, an assembly comprising a base and the ribs may be mounted to the rotor rim. The base may be configured to be mounted to the circumferential surface of the rotor rim. In some examples, the base may be slightly curved to fit the rotor rim. Manufacturability of the overall rotor rim may be easier.

[0074] Figure 5 shows a cross-section of another example of a permanent magnet rotor according to the present disclosure.

[0075] Figure 5 shows that the bolt 400 mechanically attaching the magnet module 300 to the rotor rim 200, during operation of the electrical machine, may be subjected to radial forces (RF) and to bending (B) due to the tangential forces.

[0076] Figure 5 also shows that the ribs 210, 220 of the rotor rim may comprise at least a recess. The recess may extend axially along the first and / or second lateral surfaces of the ribs. In some examples, the recess may comprise a rectangular cross-section. In some examples, the recesses may be located in a middle section of the lateral surfaces.

[0077] In some examples, the module base 300 of the permanent magnet module may comprise protruding surfaces or protrusions 315, 316 extending in an axial direction along the first and / or second lateral surfaces of the module base. In some examples, the protrusions 315, 316 may be shaped as tapered locking keys or wedges. The protrusions 315, 316 may be configured to fit into recesses of the ribs. In these examples, the recesses may be used to fix the permanent magnet modules to the rotor rim i.e. via the ribs. The recesses in the base module may be used as guiding slots during the process of mounting the permanent magnet module to the rotor rim. Assembly of the permanent magnet module 300 may be easier and a tighter fit between the permanent magnet module 300 and the rotor ribs 210, 220 may be achieved.

[0078] In further examples, as schematically represented in figure 6, the permanent magnet rotor 100 may comprise a cooling channel 415 at least arranged between one of the first and second lateral surfaces of the module base and the first and second ribs.

[0079] The cooling channels may be used for cooling the magnets in order to avoid overheating of the magnets that reduces the efficiency of the electrical machine. The cooling channels may be used to circulate air along them.

[0080] In these examples, the module base 310 of the permanent magnet module may comprise recesses, substantially matching the size and shape of recesses of the rotor rim. The recesses may extend in an axial direction along the first and / or second lateral surfaces of the module base.

[0081] The recesses of the permanent magnet module 300 and the recesses of the ribs may substantially match once the permanent magnet module 300 is mounted to the rotor rim 200, defining a cooling channel extending axially.

[0082] The permanent magnet rotor of figure 6 comprises a first cooling channel 415 arranged between the first lateral surface 312 of the module base and the first rib 210 and a second cooling channel 416 arranged between the second lateral surface 313 of the module base and the second rib 220.

[0083] In further examples (not shown), the permanent magnet module may comprise a cooling channel arranged within the module base. The cooling channel may avoid overheating of the one or more permanent magnets supported by the module base. In the examples wherein the permanent magnet module comprises a plurality of permanent magnets, one or more cooling channels may be arranged within the module base and between two magnet modules.

[0084] In some examples, as shown in figures 3 - 5, the module base 310 may comprise a bottom surface 311 and the bottom surface 311 and the first and second lateral surfaces 312, 313 of the module base may contact a rotor rim 200 surface.

[0085] In other examples, as shown in figure 6, the first and second ribs 210, 220 may only support the first and second lateral surfaces 312, 313 of the module base. In these examples, the bottom surface 311 of the module base may not be supported by the rotor rim i.e. may not contact the rotor rim.

[0086] Accordingly, a gap 418 may be arranged between the bottom surface 311 of the module base and the rotor rim surface 200. The gap may be used for mechanical purposes. In some examples, the gap may extend in an axial direction.

[0087] Even though the examples shown include a permanent magnet module with outwardly tapering walls which are supported and retained by a triangular rib, in other examples, the permanent magnet modules may have inwardly tapering walls (i.e. the module becomes thinner towards the top), which are retained and supported by ribs which may haveor include a cross-section of an inverted triangle. I .e. in such a case, the top of the triangle (of the cross-section of the rib) is at or near the rim, whereas the base of the triangle is at the air gap. The permanent magnet modules can be retained between and below two neighboring ribs.

[0088] In a further aspect of the present disclosure, a generator is provided. The generator comprises a stator and a rotor and an airgap radially arranged between the stator and the rotor. The generator further comprises a permanent magnet rotor according to any of the examples previously disclosed.

[0089] In some examples, the generator may be a wind turbine generator. In further examples, the generator may be a direct drive wind turbine generator.

[0090] This written description uses examples to disclose the teaching, including the preferred embodiments, and also to enable any person skilled in the art to practice the teaching, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

CLAIMS1. A permanent magnet rotor (100) for an electrical machine, comprising: a rotor rim (200), comprising a circumferential surface with at least a first rib (210) and a second rib (220) extending along an axial direction; and a plurality of permanent magnet modules (300) mounted on the rotor rim surface extending along an axial direction, each of the modules comprising a module base (310) supporting one or more permanent magnets (320), wherein the module base (310) comprises a first lateral surface (312) and a second lateral surface (313), and wherein a shape of the first and second lateral surfaces (312, 313) is substantially complementary to a shape of the first and second ribs (210, 220) such that the first and second ribs (210, 220) at least partially support the first and second lateral surfaces (312, 313) of the module base (310).

2. The permanent magnet rotor (100) of claim 1 , wherein the ribs (210, 220) are made of solid steel or iron.

3. The permanent magnet rotor (100) of claims 1 or 2, wherein the ribs (210, 220) have a substantially triangular cross-section.

4. The permanent magnet rotor (100) of any of claims 1 - 3, wherein the ribs (210, 220) are integrally formed with the rotor rim (200).

5. The permanent magnet rotor (100) of any of claims 1 - 4, wherein the ribs (210, 220) have a first side and a second side, and wherein the first lateral surface (312) of the module base contacts one of the first and second sides of the rib, and wherein the first and / or second side of the ribs comprises a recess extending in an axial direction, optionally wherein the first and / or second lateral surfaces (312, 313) of the module base comprise a protrusion configured to be received in the recess.

6. The permanent magnet rotor (100) of any of claims 1 - 5, further comprising a cooling channel (415, 416) at least arranged between one of the first and second lateral surfaces (312,7. The permanent magnet rotor (100) of any of claims 1 - 6, wherein the module further comprises a bottom surface (311) and a gap (418) is arranged between the bottom surface (311) of the module base (310) and the rotor rim (200) surface.

8. A permanent magnet module (300) for an electrical machine comprising: one or more permanent magnets (320), and a module base (310) configured to be attached to a rotor rim (200) and support the one or more permanent magnets (320) and comprising a first lateral surface (312) and a second lateral surface (313), wherein the first and second lateral surfaces (312, 313) of the module base are curved or inclined and extend in a radial direction towards an air gap and outwardly away from each other.

9. The permanent magnet module (300) of claim 8, wherein the permanent magnet module (300) is configured to be mounted between two ribs (210, 220) of the rotor rim (200).

10. The permanent magnet module of any of claims 8 or 9, wherein at least one of the first and second lateral surfaces (312, 313) of the module base comprises a lateral protrusion (315, 316) extending in an axial direction.

11. A rotor for a permanent magnet rotor of an electrical machine, comprising: a rotor rim (200) having an active part surface facing an air gap of the electrical machine; a plurality of ribs (210, 220) at the active part surface extending along an axial direction, and wherein the ribs (210, 220) are configured to receive a module base (310) of a permanent magnet module (300) between them.

12. The rotor of claim 11 , wherein the ribs (210, 220) taper outwardly in a radial direction towards the air gap.

13. The rotor of claim 11 or 12, wherein the ribs (210, 220) are made of solid steel or iron.

14. A generator comprising a stator and a rotor and an airgap radially arranged between the stator and the rotor, wherein the generator comprises: a permanent magnet rotor (100) according to any of the claims 1 - 7.

15. The generator of claim 14, wherein the generator is a direct drive wind turbine generator.

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