WO2008107512A1

WO2008107512A1 - Pole module for rotor of electric machine and rotor of electric machine

Info

Publication number: WO2008107512A1
Application number: PCT/FI2008/000035
Authority: WO
Inventors: Ville Voutilainen; Ari Vartiainen; Mikko Salmi; Juhani Mantere; Risto Pulkkinen; Antti MÄKINEN
Original assignee: Abb Oy
Priority date: 2007-03-02
Filing date: 2008-03-03
Publication date: 2008-09-12
Also published as: FI119960B; FI20070183A; FI20070183A0; CN201444598U

Abstract

The object of the invention is a pole module (30) for the rotor of an electrical machine and a corresponding rotor. According to the invention, the pole module (30) comprises a non-magnetic body part (2') equal in width to at least two rotor poles (8) and at least two sheet packs (10) attached to the body part (2') that constitute corresponding poles (8) of the rotor. In the pole module (30), a permanent magnet piece (18) is fitted in the space between two adjacent sheet packs (10).

Description

POLE MODULE FOR ROTOR OF ELECTRIC MACHINE AND ROTOR OF ELECTRIC MACHINE

The object of the invention is a pole module for the rotor of an electrical machine according to the preamble part of Claim 1, and a rotor for an electrical machine according to the preamble part of Claim 8.

In a permanent-magnet synchronous machine, the excitation field is generated using permanent magnets installed in the machine's rotor. The permanent magnets are either fitted on the surface of the rotor facing the air gap, or the permanent magnets are embedded into the rotor's magnetic core. The magnetic core is most often manufactured of ferromagnetic iron sheets assembled into sheet packs extending throughout the rotor's length. The design criteria for dimensioning the permanent magnets and sheet packs is the excitation power required by the electrical machine. The mechanical structure and the fastening of different components are affected by factors such as the forces imposed on them and the size of the electrical machine.

Excitation arrangements impose special requirements on electrical machines having a high number of poles and a large rotor diameter, particularly on machines with a small slot factor and concentrated stator winding. In these machines, the slot factor is q < 1, the slot factor being defined as q = Q/(m*2*p), in which Q refers to the number of slots, m to the number of phases and p to the number of pole pairs in the machine. Concentrated winding refers to a stator winding in which the winding is coiled around one tooth of the stator. Due to the high number of poles, the space corresponding to one magnetic pole in the circumferential direction of the rotor is small. The radial passage for the magnetic flux is narrow. It is often not possible to use a surface magnet mentioned above because surface magnets cannot provide a sufficient magnetic flux density for heavily loaded drives.

The fastening of the permanent magnets and magnetic cores must be arranged reliably in order not to disrupt the flow of the magnetic flux. Good efficiency of a permanent-magnet electrical machine also requires that the stray flux is minimised. It is difficult to handle magnetic cores of a large diameter during the manufacture of an electrical machine, which means that the production and manufacturing technique must be planned in advance to allow components to be pre-manufactured as smaller parts that are easier to handle. The purpose of the present invention is to create an efficient and advantageous rotor pole structure for a large-diameter electrical machine. In order to achieve this, the pole module according to the invention is characterised by the features specified in the characteristics section of Claim 1. The rotor according to the invention is characterised by the features specified in the characteristics section of Claim 8. Certain other preferred embodiments of the invention are characterised by the features of the dependent claims.

In the solution according to the invention, the pole structure of the electrical machine's rotor is formed of several pole modules attached on the outer surface of the rotor consecutively in the circumferential direction. The magnetic sheet packs for the pole modules can be manufactured separately. This makes them easier to handle and allows them to be separately manufactured to completion. The solution according to the invention will substantially reduce the number of components to be installed on the rotor centre and the number of bores to be made to the rotor centre. The rotor manufacturing time at assembly and the installation time at the plant will also be substantially reduced. The solution also facilitates the automation of manufacturing and assembly.

The solution according to the invention makes the manufacture of the body structure substantially simpler and easier as the body structure is made of aluminium by extrusion and does not need machining. Furthermore, the structure according to the invention minimises stray flux between poles, which improves the efficiency of the machine.

With the rotor according to the invention, the core section of the rotor's magnetic circuit is formed of modules fitted on the outer circumference of the rotor; at least two permanent magnets are fittable to each module in the circumferential direction of the rotor, the module constitutes two poles, and the pole modules are attachable to the rotor centre. The rotor manufacturing time and particularly the assembly time at the plant are reduced as complete pole modules can be attached to the rotor centre.

According to a preferred embodiment of the invention, the width of the pole module corresponds to four rotor poles. Body structure modules can thus be attached to the rotor centre at equal intervals in the circumferential direction, placing attachment screws below every other permanent magnet.

According to a preferred environment, the pole module is attachable to the rotor centre by its body structure between the sheet packs. This allows the body structure to be attached without the permanent magnets, which are installable later in the radial direction of the rotor, for example, and lockable into place using an attachment strip fitted into grooves on the sheet packs. The permanent magnets can be unexcited during installation, which makes them easier to handle, and the permanent magnets will be excited in the correct direction after being fitted in place. On the other hand, pre-excited permanent magnets can also be used within the scope of the invention. The attachment strip fitted on top of the permanent magnets not only supports the permanent magnets against centrifugal forces but also protects them from dirt and corrosion.

According to a preferred feature of the environment, the sheet pack and body part are interlocked using a shape-locking joint. Useful and functional joints include particularly a dovetail joint or T slot joint, with several examples in prior art. In connection with the present invention, they enable functional and practical assembly and flexible variation in the order of assembly. The sheet pack can be fitted to the body part in whole or as shorter sections, even one sheet at a time.

According to another preferred feature, the non- magnetic body part is aluminium. Aluminium is feasible as a body part material based on its electrical, magnetic and strength properties. Extrusion makes it easy and inexpensive to manufacture an aluminium component of sufficient dimensional accuracy.

According to a preferred embodiment, the rotor centre is non-magnetic and electrically conductive, which means that the rotor centre also serves as a damping winding that damps the pulsing flux and reduces losses arising from this. Thanks to its thermal conductivity, the aluminium body part also facilitates cooling of the rotor.

In the following the invention will be described in more detail with the help of certain embodiments by referring to the enclosed drawings, where

- Figure 1 illustrates a pole module according to the invention,

- Figure 2 illustrates a pole module according to the invention installed on a rotor, and

- Figure 3 illustrates another pole module according to the invention installed on a rotor. Figure 1 illustrates a pole module according to the invention viewed from the module end. The width of the module in the circumferential direction of the rotor corresponds to three magnetic poles, and it has a body structure 2 made of aluminium by extrusion. The length of the module in the axial direction of the machine corresponds to the length of the rotor. The inner surface 4 of the body structure is slightly curved, corresponding to the cylindrical outer surface of the rotor centre. In the circumferential direction of the rotor, one end of the body structure 2 has a mounting notch 3, and the other end has a corresponding mounting projection 5. The outer surface of the module's body structure has dovetail-shaped projections or dowels 6 at each magnetic pole 8. A corresponding dovetail joint notch 12 is formed at the lower edge of the sheet pack 10 made of magnetically conductive sheets. The sheet packs 10 constitute the magnetic rotor core. The rotor cores are excited with permanent magnets placed between them so that in the circumferential direction, N and S poles are formed alternately. The top edge of these forms the rotor's outer surface that faces the air gap of the electrical machine. Preferably the side walls 14 of the sheet packs are cut slightly diagonally so that a rectangular space 15 for a permanent magnet remains between adjacent sheet packs. Bores 11 for attachment bolts are drilled in the body structure at the space 15. In the longitudinal direction of the rotor, there are several bores 11 and, correspondingly, bolts fitted in the bores in order to attach the module reliably to the rotor. The outermost part of the side walls 14 of the sheet packs contains narrow attachment grooves 16 into which the attachment strips 20 (Figure 2) for permanent magnets 18 are fitted after the permanent magnets have been put in place. Bores 22 are drilled in the rotor cores, and threaded rods 24 fitted in the bores are used to compress the sheets of the rotor core with the help of pole end plates 26.

Figure 2 illustrates the pole module 30 attached to the rotor centre 28. The pole module 30 has four poles but otherwise corresponds to the module in Figure 1, and the parts corresponding to each other carry the same reference numbers in Figures 1 and 2.

During the manufacture of the rotor, sheet packs 10 constituting the rotor core are attached to the body structure of the pole module with a dovetail joint. The sheets for the sheet packs are manufactured, for example, by cutting them into the correct shape with a sheet cutter. The sheet packs are tightly compressed together using end plates 26 fitted at the ends and threaded rods 24 going through the sheet packs. The body part 2' of each pole module is attached to the rotor centre 28 in the circumferential direction using two bolts 32 fitted into bores 34 between the pole cores. The number of attachment bolts 32 in the axial direction of the rotor depends on the length of the rotor. The curvature of the bottom 31 of the pole module body part 2' corresponds to the curvature of the surface of the outer circumference of the rotor centre 28. The bolts 32 are fitted at the two outermost openings for permanent magnets 18 in the pole module. One side of the pole module has a mounting notch 38 in the circumferential direction of the rotor, and the other side has a corresponding mounting projection 40 for mutual alignment and support of the pole modules. When the pole module is attached in place, permanent magnets 18 are fitted to it in the radial direction of the rotor between the sheet packs 10. Thus some of the permanent magnets are between the sheet packs of a single pole module, while some are between the outermost sheet packs of two adjacent pole modules. The permanent magnets are glued to the pole module, and an attachment strip 20 is fitted in attachment grooves 16 made for the purpose on the side of the permanent magnets facing the air gap. The attachment strips support the permanent magnets against centrifugal forces and pfotect 'thefή⁰ against corrosion and other detrimental effects of the environment.

The inventive idea also includes the assembly of pole modules directly on the surface of the rotor centre, meaning that the body part is first attached to the rotor centre, after which the sheet packs and subsequently the permanent magnets are fitted in place. In this case, the body parts can also be attached at the position of the sheet pack.

Figure 3 illustrates an embodiment of the invention in which the attachment of the sheet packs and body part deviates from the embodiment of Figure 2. To the applicable extent, the reference numbers in Figure 3 correspond to the numbering used previously. A T- shaped dowel 44 is formed in the body part 42 and, correspondingly, a fitting T-shaped slot

46 is formed in the sheet pack 43. Binders 48 are formed on the outermost edge of the side wall of the sheet pack for the purpose of supporting the permanent magnets 18 against centrifugal forces. In this embodiment, the permanent magnets 18 are installed in the axial direction of the rotor either in openings between the sheet packs or simultaneously with the sheet packs 43. To protect against corrosion, the outer surface 45 of the permanent magnets is coated with lacquer or resin, for example. The body part 42 is attached with screws 50 extending through the rotor centre 52, which are tightened from the inside of the rotor centre 52. The embodiments illustrated in Figures 2 and 3 can also be combined as applicable to implement the inventive idea. The attachment between the sheet pack and body part can also be made using end plates, in which case the end plates are bolted also to the ends of the body part. Instead of what is described above, the attachment between adjacent body parts can also be curved or completely or partially bevelled, for example.

The number of poles in a rotor according to the invention is high, at least more than ten. The solution according to the invention is used to efficiently implement rotors with dozens of poles or even more than one hundred poles. The rotor according to the invention is particularly feasible for electrical machines with a concentrated winding, which means that the winding layer is wound around a single tooth.

The invention has been described above with the help of certain embodiments. However,, the description should not be considered as limiting the scope of patent protection; the embodiments of the invention may vary within the scope of the following claims. For example, the body part of the pole module may extend in the circumferential direction to the boundary between the sheet pack and permanent magnet. When the pole module is assembled directly on the rotor centre, the attachment between body parts can also be at the position of the sheet pack.

Reference numbers: 2, 2' body structure; 3 mounting notch; 4 inner surface of body structure; 5 mounting projection; 6 dovetail dowel; 8 magnetic pole; 10 sheet pack; 11 bore for attachment bolt; 12 dovetail notch; 14 side wall of sheet pack; 15 space for permanent magnet; 16 attachment groove; 18 permanent magnet; 20 attachment strip; 22 bore; 24 threaded rod; 26 end plate; 28 rotor centre; 30 pole module; 31 bottom of body part; 32 attachment bolt; 34 bore; 38 mounting notch; 40 mounting projection; 42 body part; 44 T- shaped dowel; 45 outer surface of permanent magnet; 46 T-shaped slot; 48 binder; 50 screw; 52 rotor centre

Claims

1. A pole module (30) for the rotor of an electrical machine, characterised in that the pole module (30) comprises a non-magnetic body part (2, 2') equal in width to at least two rotor poles (8) and at least two sheet packs (10) attached to the body part (2, 2') that constitute at least two poles (8) of the rotor, whereby a space (15) remains between two adjacent sheet packs (10) in the pole module (30), into which space a permanent magnet piece (18) can be fitted.

2. A pole module according to Claim 1, characterised in that the pole module (30) is equal in width to four rotor poles (8).

3. A pole module according to Claim 1, characterised in that the pole module (30) is attachable to the rotor centre (28) by its body part (2, 2') between the sheej -packs.' .':-.."..^•■.^■-."

4. A pole module according to Claim 3, characterised in that the permanent magnets (18)is installable to the pole module (30) in the radial direction of the rotor after attachment of the pole module (30), and is lockable in place using attachment strips (20).

5. A rotor according to any of the preceding Claims, characterised in that the sheet pack (10) and the body part (2, 2') are interlocked using a shape-locking joint (6, 12).

6. A rotor according to Claim 5, characterised in that the sheet pack and body part are interlocked using a dovetail joint (6, 12) or a T slot joint (44, 46).

7. A rotor according to any of the preceding Claims, characterised in that the non- magnetic body part (2, 2') is aluminium.

8. A rotor for an electrical machine excited by permanent magnets, the magnetic circuit of which comprises a core part formed of a magnetically conductive sheet pack (10) into which permanent magnets (18) are fitted, the number of poles of the electrical machine being high, characterised in that the core part is formed of modules (30) fitted on the outer circumference of the rotor; at least two permanent magnets (18) are fittable to each module (30), the module correspondingly constitutes at least two poles (8), and the pole modules (30) are attachable to the rotor centre (28).

9. A rotor according to Claim 8, characterised in that the pole modules (30) comprise a sheet pack (10) and a non- magnetic body part (2, 2') attached to it.

10. A rotor according to Claim 9, characterised in that the non-magnetic body part (2, 2') is electrically and thermally conductive.

11. A rotor according to any of the Claims from 8 to 10, characterised in that the pole modules (30) comprise openings (15) facing the outer circumference of the rotor for permanent magnets (18) and that the openings (15) are closable with attachment strips (20).