Permanent magnet modules for permanent magnet motors

Abstract

The present invention describes a permanent magnet module (101, 102) for a permanent magnet motor (10). The permanent magnet module (101, 102) comprises at least a permanent magnet (200) and a base plate (301, 302), the base plate (301, 302) comprising at least a first portion (400) and a second portion (501, 502), the first portion (400) providing an interface for attaching the permanent magnet module (101, 102) to the permanent magnet motor (10), and the second portion (501, 502) being attached to at least one permanent magnet (200), wherein the second portion (501, 502) has a structure for reducing eddy current losses or comprises a material for reducing eddy current losses.

Description

Technical Field

[0001] The present invention relates to the field of reducing eddy current losses in permanent magnet electric machines. In particular, the present invention relates to a permanent magnet module comprising a support and a magnet for a permanent magnet electric machine. Background Art

[0002] An electrical machine, such as a generator installed in a wind turbine, typically comprises a rotor that rotates relative to a stator about an axis of rotation. The stator and rotor are separated from each other by an air gap that extends circumferentially around the axis of rotation.

[0003] In a permanent magnet motor, the rotor includes a plurality of permanent magnet modules, each module comprising a base plate and one or more permanent magnets attached to the base plate. The base plate is attached to the rotor body so that, during operation, it is interposed between the corresponding magnet and the rotor body. In each magnet module, a cover plate is typically positioned above the permanent magnet(s) to encapsulate the permanent magnet(s). The cover plate can be made of stainless steel or any other non-magnetic material and is welded or otherwise secured to the corresponding base plate. The stator typically comprises a body having radial stator slots extending longitudinally in the axial direction of the stator, and an electrical circuit comprising a plurality of copper windings housed in the slots.

[0004] In permanent magnet wind turbine generators, the permanent magnet modules mounted on the rotor body are subjected to high magnetic fields of varying magnitude and frequency, which results in high iron losses in any conductive steel components. Specifically, eddy currents are induced by the asynchronously rotating fields in the air gap. These losses increase the temperature inside the generator, which reduces torque and power performance. They also lower the generator's efficiency and, consequently, the annual energy production (AEP).

[0005] In permanent magnet motors, laminated materials can be used in the baseplate to reduce eddy current losses. However, such materials are expensive and significantly reduce the mechanical strength of the magnet modules. Alternatively, soft magnetic composite (SMC) materials can be used in the baseplate, but this prevents the cover from being welded to the baseplate. This requires different fixing solutions, which may be more expensive or less practical.

[0006] Therefore, it is desirable to provide efficient and cost-effective techniques that can improve the construction characteristics of permanent magnet modules and reduce overall losses in permanent magnet electric machines. Summary of the Invention

[0007] This object can be solved by a permanent magnet module according to the independent claim.The dependent claims describe advantageous embodiments of the invention.

[0008] According to the present invention, a permanent magnet module for a permanent magnet motor is provided. The permanent magnet module includes at least a permanent magnet and a base plate. The base plate includes at least a first portion and a second portion. The first portion provides an interface for attaching the permanent magnet module to the permanent magnet motor. The second portion is attached to at least one permanent magnet. The second portion has a structure for reducing eddy current losses or includes a material for reducing eddy current losses.

[0009] According to a possible embodiment of the present invention, the permanent magnet electrical machine may be a generator. In particular, but not exclusively, the generator may be used in a wind turbine.

[0010] Advantageously, the present invention proposes using alternative types of materials in the upper, second portion of the baseplate (i.e., the portion to which the permanent magnets are attached). This can be particularly advantageous in permanent magnet machines (i.e., concentrated winding or fractional slot generators) where rotor losses are particularly high. The first, lower portion (which attaches it to the permanent magnet machine, such as the rotor body of the generator) can be effectively designed to provide mechanical strength.

[0011] According to one embodiment of the invention, the second part of the base plate is laminated. The laminate forms the second part of the base plate and is fixed (by means of glue or other means) to the solid first part of the base plate.

[0012] According to another embodiment of the present invention, the second portion of the base plate comprises a soft magnetic composite (SMC) material. The SMC is secured (by adhesive or other means) to the solid first portion of the base plate. The SMC material has a much higher resistivity than standard-grade steel, which reduces iron losses to zero by providing a higher resistance to eddy currents.

[0013] In both of the aforementioned embodiments, the lower first portion of the baseplate remains identical, ensuring that the material or structure of the second portion does not affect the assembly of the module within the rotor body. Specifically, it does not affect mechanical strength. Furthermore, the laminate or SMC material significantly contributes to reducing eddy current losses in permanent magnet motors.

[0014] According to another embodiment of the present invention, at least the second portion of the base plate comprises high-silicon steel having a composition comprising between 2% and 4% silicon. High-silicon steel has a resistivity 4-6 times that of standard grade steel. High-silicon steel reduces iron losses by at least 50% by providing higher resistance to eddy currents. The mechanical properties of high-silicon steel (e.g., Young's modulus, yield strength hardness, density, etc.) are similar to (or even higher than) standard steel, and this will not affect the structural performance of the component. The first portion of the base plate may also comprise high-silicon steel having a composition comprising between 2% and 4% silicon. Specifically, at least the second portion of the base plate may comprise 60Si2Mn or equivalent (according to different nomenclature) steel.

[0015] According to an embodiment of the present invention, the permanent magnet module includes a cover plate for at least partially covering the permanent magnets, the cover plate being attached to at least a first portion of the base plate. Advantageously, the structure and material of the second portion of the base plate do not affect the fixing of the cover plate to the first portion of the base plate (by welding or other means).

[0016] According to an embodiment of the present invention, the cover plate and the first portion of the base plate comprise stainless steel.

[0017] Advantageously, since the electrical conductivity of stainless steel is lower than that of carbon steel, losses in the base plate are significantly reduced. The term "carbon steel" is used to refer to steel that is not stainless steel, and in this context, "carbon steel" may include alloy steels. Ferritic stainless steel does not significantly affect the reluctance of the magnetic circuit because it has a high magnetic permeability and therefore still provides a low reluctance path for the magnetic flux. Stainless steel does not corrode in the environment inside the wind turbine, so no coating or paint layer is required. The welding process between the two components of the same material (the cover plate and the first part of the base plate) is easier to control and allows for high-quality welds. Therefore, it is expected that the occurrence of welding problems between the base plate and the magnet cover plate will be reduced. The second part of the base plate may also comprise stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

[0019] Figure 1 Shown is a schematic cross section of a wind turbine comprising an embodiment of the invention.

[0020] Figure 2 A cross-sectional view is shown of a permanent magnet electrical machine including a plurality of permanent magnet modules according to the present invention.

[0021] Figure 3 A front circumferential view of a permanent magnet module according to a first exemplary embodiment of the present invention is shown.

[0022] Figure 4 A front circumferential view of a permanent magnet module according to a second exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] The illustrations in the drawings are schematic. It should be noted that in different figures, similar or identical elements are provided with the same reference signs.

[0024] Figure 1A partial cross-sectional view of a wind turbine 1 is shown which includes a permanent magnet motor 10 (i.e. a generator) which includes a permanent magnet module according to the invention. The permanent magnet motor 10 includes a stator 11 and a rotor 12. The rotor 12 is rotatable relative to the stator 11 about the longitudinal axis of the permanent magnet motor 10. In the following text, the terms axial, radial and circumferential are intended to refer to the longitudinal rotation axis Y of the permanent magnet motor 10. Figure 1 In the embodiment shown, the rotor 12 is radially outside 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 shown in the drawings), the rotor 12 is radially inside the stator 11 and rotatable about the longitudinal axis Y. The permanent magnet motor 10 may be a fractional-slot concentrated winding generator.

[0025] According to other possible embodiments of the present invention (not shown in the drawings), the present invention can be applied to any type of permanent magnet motor, such as radial permanent magnet motor, axial permanent magnet motor, etc. The present invention can also be applied to an integer-slot permanent magnet motor.

[0026] Multiple permanent magnet modules ( Figure 1 The rotor 12 is attached to the rotor 12 by means of corresponding base plates, as will be described in detail below. According to other possible embodiments of the invention (not shown in the drawings), a plurality of permanent magnet modules can be attached to the stator of a permanent magnet motor.

[0027] Figure 2 A partial cross-sectional view of a permanent magnet motor 10 is shown, which includes a plurality of permanent magnet modules 101, 102 attached to a rotor 12. The permanent magnet modules 101, 102 are attached to the side of the rotor 12 facing the stator 11. Each permanent magnet module 101, 102 includes a permanent magnet 200 and a base plate 301, 302. According to other embodiments of the present invention (not shown), each permanent magnet module 101, 102 may include more than one permanent magnet 200 and more than one base plate 301, 302. Each of the permanent magnets 200 is attached to the rotor body 130 of the rotor 12 by means of a corresponding base plate 301, 302. Each base plate 301, 302 of each permanent magnet module 101, 102 is connected to a corresponding recess 131 provided in the rotor body 130.

[0028] Figure 3A tangential cross-sectional view of a permanent magnet module 101 is shown, comprising permanent magnets 200 and a corresponding base plate 301 attached to the permanent magnets 200. The base plate 301 includes a first portion 400, which provides an interface for attaching the permanent magnet module 101 to a corresponding recess 131 in the rotor body. The base plate 301 includes a second portion 501, which is attached to the first portion 400 on a first side and to the permanent magnets 200 on a second contact side 120 opposite the first side. Tangentially, the first portion 400 is larger than the second portion 501, with a step provided between them. The second portion 501 is laminated. The permanent magnet module 101 includes a cover plate 601 that covers the permanent magnets 200. The cover plate 601 is welded to the first portion 400 of the base plate 301. Both the cover plate 601 and the first portion 400 of the base plate 301 are made of stainless steel.

[0029] Figure 4 A tangential cross-sectional view of a permanent magnet module 102 is shown, which includes a permanent magnet 200 and a corresponding base plate 302 attached to the permanent magnet 200. The base plate 302 includes a first portion 400 that provides an interface for attaching the permanent magnet module 102 to a corresponding recess 131 in the rotor body. The base plate 302 also includes a second portion 502 that is attached to the first portion 400 on a first side and to the permanent magnet 200 on a second contact side 120 opposite the first side. The second portion 502 includes a soft magnetic composite material (SMC). Alternatively, according to another embodiment of the present invention, the second portion 502 of the base plate 302 includes high silicon steel having a composition comprising between 2% and 4% silicon. For example, the second portion 502 of the base plate 302 can include 60Si2Mn steel or an equivalent steel.

Claims

1. A permanent magnet module for a permanent magnet motor (10), the permanent magnet module comprising at least a permanent magnet (200) and a base plate, the base plate comprising at least a first portion (400) and a second portion, the first portion (400) providing an interface for attaching the permanent magnet module to the permanent magnet motor (10), and the second portion being attached to at least one permanent magnet (200), wherein: The second portion has a structure for reducing eddy current loss or includes a material for reducing eddy current loss, wherein the permanent magnet module includes a cover plate (601) for at least partially covering the permanent magnet (200), the cover plate (601) is attached to at least the first portion (400) of the base plate, and wherein the cover plate (601) and the first portion (400) of the base plate include stainless steel.

2. The permanent magnet module according to claim 1, wherein At least the second portion of the base plate is laminated.

3. The permanent magnet module according to claim 1 or 2, wherein: At least the second portion of the base plate comprises a soft magnetic composite material.

4. The permanent magnet module according to claim 1 or 2, wherein: At least the second portion of the base plate comprises high silicon steel having a composition comprising between 2% and 4% silicon.

5. The permanent magnet module according to claim 4, wherein: At least the second portion of the base plate comprises 60Si2Mn or equivalent steel.

6. A permanent magnet motor (10) comprising a plurality of permanent magnet modules, each of the plurality of permanent magnet modules being a permanent magnet module according to any one of claims 1 to 5.

7. A wind turbine (1) comprising a permanent magnet electrical machine (10) according to claim 6.

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