Abstract
A permanent magnet module for a permanent magnet machine is provided, the permanent magnet module including a baseplate, at least a permanent magnet attached to the baseplate and a cover for at least partially covering the permanent magnet. The cover includes a stainless steel having a high magnetic permeability.
Claims
1. A permanent magnet module for a permanent magnet machine, the permanent magnet module comprising: a baseplate; a permanent magnet attached to the baseplate; and a cover for at least partially covering the permanent magnets, wherein the cover includes a stainless steel having a high magnetic permeability.
2. The permanent magnet module according to claim 1, wherein the cover includes a martensitic stainless steel.
3. The permanent magnet module according to claim 2, wherein the permanent magnet includes a bottom surface facing the baseplate and a top surface opposite to the bottom surface and at least a lateral surface connecting the bottom surface with the top surface, the cover at least partially covering the top surface and the lateral surface, the magnetic permeability of the cover the top surface being higher than the magnetic permeability of the cover at the lateral surface.
4. The permanent magnet module according to claim 1, wherein the cover includes a ferritic stainless steel.
5. The permanent magnet module according to claim 1, wherein the cover is attached to the baseplate, the baseplate including a same material of the cover.
6. The permanent magnet module according to claim 5, wherein the cover is welded to the baseplate.
7. The permanent magnet machine including a plurality of permanent magnet modules according to claim 1.
8. A wind turbine comprising an electrical generator according to claim 7.
Description
BRIEF DESCRIPTION Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:
[0012] FIG. 1 shows a schematic section of a wind turbine including embodiments of the present invention;
[0013] FIG. 2 shows a cross-sectional view of a permanent magnet machine including a plurality of permanent magnet modules according to the present invention;
[0014] FIG. 3 shows a frontal circumferential view of a permanent magnet module according to a first exemplary embodiment of the present invention;
[0015] FIG. 4 shows a frontal circumferential view of a permanent magnet module according to a second exemplary embodiment of the present invention; and
[0016] FIG. 5 shows a frontal circumferential view of a permanent magnet module according to a third exemplary embodiment of the present invention.
DETAILED DESCRIPTION
[0017] FIG. 1 shows a partial cross-sectional view of a wind turbine 1 comprising a tower 2 which is mounted on the ground at one end and a nacelle 3 which is mounted at the opposite end of the tower 2. The nacelle 3 is rotatably mounted over the tower 2. The nacelle 3 accommodates a permanent magnet machine 10, i.e., an electrical generator, which includes a plurality of permanent magnet modules according to embodiments of the invention. Furthermore, the wind turbine 10 comprises a hub 5 which is rotatable about a rotor axis Y. When not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotor axis Y. The wind turbine 1 further comprises at least one blade 4 (in the embodiment of FIG. 1, the wind rotor comprises three blades 4, of which only two blades 4 are visible) mounted on the hub 5. The blades 4 extend substantially radially with respect to the rotational axis Y. The permanent magnet machine 10 includes a stator 11 and a rotor 12. The rotor 12 is rotatable with respect to the stator 11 about a longitudinal axis of the permanent magnet machine 10. The terms axial, radial and circumferential in the following are to be intended with reference to the longitudinal axis Y of rotation of the permanent magnet machine 10. In the embodiment of FIG. 1, the rotor 12 is radially external with respect the stator 11 and rotatable about the longitudinal axis Y. A circumferential air gap is provided between the stator 11 and the rotor 12. According to other possible embodiments of the present invention (not represented in the attached figures), the rotor 12 is radially internal with respect the stator 11 and rotatable about the longitudinal axis Y. The permanent magnet machine 10 may be a fractional slot concentrated winding electrical generator.
[0018] According to other possible embodiments of the present invention (not represented in the attached figures), the present invention may be applied to any type of permanent magnet electric machines, e.g., radial, axial, etc. Embodiments of the present invention may be applied also to integral-slot electric permanent magnet machine.
[0019] A plurality of permanent magnets modules (not visible in FIG. 1) is attached to the rotor 12 by respective baseplates, as detailed in the following. According to other possible embodiments of the present invention (not represented in the attached figures), a plurality of permanent magnets modules may be attached to the stator of a permanent magnet machine.
[0020] FIG. 2 shows a partial cross-sectional view of the permanent magnet machine 10 including a plurality of permanent magnet modules 101 attached to the rotor 12. The permanent magnet modules 101 are attached to a side of the rotor 12 which faces the stator 11. Each permanent magnet module 101 comprises a permanent magnet 200 and a baseplate 301. According to other embodiment of the present invention (not shown), each permanent magnet module 101 may comprise more than one permanent magnet 200 and more than one baseplate 301. Each of the permanent magnets 200 is attached to a rotor body 130 of the rotor 12 by the respective base plate 301. Each base plate 301 of each permanent magnet module 101 is connected to a respective recess 131 provided in the rotor body 130.
[0021] FIG. 3 shows a tangential sectional view of a permanent magnet module 101 including a permanent magnet 200 and a respective baseplate 301 attached to the permanent magnet 200. The permanent magnet 200 includes a bottom surface 201 facing the baseplate 301. The bottom surface 201 may be attached to the baseplate 301, for example by gluing. The permanent magnet module 101 further includes a cover 601 covering the permanent magnet 200. The cover 601 and the baseplate 301 are both made of stainless steel. The cover 601 and the baseplate 301 may be both made of the same stainless steel. The cover 601 includes a martensitic stainless steel. According to other embodiments of the invention, the cover 601 may include a ferritic stainless steel. The cover 601 is welded to the baseplate 301. According to other embodiments of the present invention, the cover 601 may be attached to the baseplate 301 by other means. The permanent magnet 200 includes a top surface 202 opposite to the bottom surface 201 and at least a lateral surface 203 connecting the bottom surface 201 with the top surface 202. The cover 601 covers the top surface 202 and the lateral surface 203. The magnetic permeability of the cover 601 at the top surface 202 is higher than the magnetic permeability of the cover 601 at the lateral surface 203. With martensitic stainless steel the difference between magnetic permeability at different portions of the cover 601 may be obtained with respective different heat treatments. If ferritic stainless steel is used, the magnetic permeability will be the same throughout all the cover 601. The permanent magnet 200 has a rectangular shape in the tangential sectional view of FIG. 3, right angle edges 204 being provided between the top surface 202 and the lateral surface 203. Consequently, also the cover 601 in the transition between the top surface 202 and the lateral surface 203 comprises respective right-angle edges.
[0022] FIG. 4 shows a tangential sectional view of a second embodiment of a permanent magnet module 101 including a permanent magnet 200 and a respective baseplate 301 attached to the permanent magnet 200. The second embodiment differentiates itself from the first embodiment of FIG. 3 in that curved edges 205 are provided between the top surface 202 and the lateral surface 203. Consequently, also the cover 601 in the transition between the top surface 202 and the lateral surface 203 comprises respective curved edges.
[0023] FIG. 5 shows a tangential sectional view of a third embodiment of a permanent magnet module 101 including a permanent magnet 200 and a respective baseplate 301 attached to the permanent magnet 200. The third embodiment differentiates itself from the first and second embodiments of FIG. 3 in that chamfered edges 205 are provided between the top surface 202 and the lateral surface 203. Consequently, also the cover 601 in the transition between the top surface 202 and the lateral surface 203 comprises respective chamfered edges.
[0024] Different shapes of the permanent magnet 200 and consequently of the cover 601 may be used to optimize the magnetic flux of the permanent magnet machine 10, in particular by minimizing the flux leakages.
[0025] Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.
[0026] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.
