WO2000070725A1

WO2000070725A1 - Rotating electrical machine

Info

Publication number: WO2000070725A1
Application number: PCT/SE2000/000952
Authority: WO
Inventors: Bengt Rydholm; Freddy Magnussen; Svante SÖDERHOLM; Sven Karlsson
Original assignee: Abb Ab
Priority date: 1999-05-12
Filing date: 2000-05-12
Publication date: 2000-11-23
Also published as: SE9901738D0; SE9901738L; AU4965500A

Abstract

The present invention relates to a rotating electrical machine. The machine comprises a stator (21) including a hollow cylindrical-shaped stator core (28) of magnetic material provided with a spooled stator winding (27) as well as a rotor (22) with flux-generating parts in the form of permanent magnets (26). The rotor includes a rotation body that is designed as a cavity between an axially extending inner rotor (29) and an outer rotor (25) where one of each ends is joined with an end section (32). In the cavity, the stator core (28) with axial winding (27) is arranged with inner and outer active air gaps (30, 31) between the rotor and the stator core. The machine is primarily intended to be used as a permanent magnet motor.

Description

Rotating Electrical Machine

TECHNICAL FIELD

The present invention relates to a rotating electrical machine. The machine comprises a stator that includes a hollow cylindrical-shaped stator core of magnetic material provided with a stator winding as well as a rotor that interacts with the stator and with flux-generating parts in the form of permanent magnets. The machine is primarily intended to be used as a permanent magnetic motor.

In the text that follows, the term rotating electrical machine should be understood as a rotating electrical machine that transforms an electrical output to mechanical output and vice versa, plus that it can function as a power capacitor, which means that it can be used to create only reactive power.

PRIOR ART A rotating electrical machine with a toroid-shaped stator is often referred to according to the terminology that is based on the prior art for a "torus" machine. There are several articles that describe such machines and a number of prototypes machines have been produced. One common factor for the described machines and the manufactured prototypes is that they generally concern permanent magnetised machines with output up to the order of 10 kW. A typical such machine is described in a publication presented at the IEEE/KTH Stockholm Power Tech Conference, Stockholm, Sweden, June 18-22, 1995, titled "The Torus Generator" by the author B.J. Chalmers. The machine will be described briefly based in Figure 1. The stator of the machine comprises a toroid-shaped core 1 wound with strip steel and with a rectangular cross- section. The core is provided with a stator winding 2 that can be designed with any number of phases. The stator is attached at the casing 3 of the machine. The rotor includes two circular moving iron disks 5 and 6 on a horizontally mounted axle 4, where the disks are located on either side of the core and are provided with axially polarised permanent magnets 7 and 8 that face towards the stator. This means that the machine has two air gaps 9 and 10 located on either side of the stator. The machine of B.J. Chalmers can be designed either as an alternating current generator or as a brushless continuous direct current machine. It is primarily intended to be used as a generator in a standby unit.

Figure 2 shows a perspective view of a similar torus machine described in an article titled "Optimum Cad-Cae Design of Axial flux Permanent magnets Motors" by F. Caricchi et al published in ICEM 92, Vol. 2, pp 637-641. In this embodiment, the laminated toroid-shaped stator 11 with a rectangular cross-section is provided with a three-phase winding 12. The two moving magnetical disks 13 and 14 attached to the rotor axle on either side of the stator are provided with permanent magnets 15 with alternating N and S poles facing towards the stator. The permanent magnets on both disks are also arranged in an axial direction so that the N poles respective S poles face one another as indicated in Figure 3. This means that the flux that is shown with dashed lines in Figure 3 goes out axially from a N pole, passes the air gap and forces its way into the armature winding and part of the way into the stator. The flux then divides itself into two halves and goes transversally in the stator towards the nearest adjacent S poles situated to either side of the N pole, before swinging off and exiting the armature winding, once more passing the air gap and out towards the S poles. The magnetic circuits are then completed via the moving iron disks.

In IEEE Trans on Industry Applications, Vol. 28, No. 3 May /June, 1992, pp 646-651, an article by C. Jensen et al is presented that describes "A Low-Loss

Permanent Brushless dc Motor Utilizing Tape Wound Amorphous Iron' ' . This motor is essentially designed like the machines described above; a torous machine with a toroid- shaped stator with a rectangular cross-section and a core made of amorphous strips. All of the machines described above are axial field machines with horizontally mounted axles. The published CA-application 2059085 A describes a vertically mounted direct current homopolar machine that can be considered to have certain similarities with the machine according to the invention, but which on close inspection is shown to be quite unlike it. The apparent superficial similarity arises in that the machine has permanent magnets in the form of two ring-shaped shells that together form a hollow stationary stator. The shell is fixed in such a way that a vertical cylindrical gap is formed between them. A cylindrical, tube-shaped rotor mounted concentrically on the axle of the machine rotates in the cylindrical gap of the stator. The motor is made of non-magnetic and electrically conducting material, such as copper, for example.

DESCRIPTION OF THE INVENTION The present invention relates to a rotating electrical machine with a new design of rotor and stator with its windings. The object of the invention is to improve the motor through obtaining a larger moment per unit of volume as well as low losses.

According to the invention, the stator includes a hollow cylindrical-shaped core of magnetisable material with a spooled stator winding. The rotor includes a rotation body comprising an axially extending inner rotor and an axially extending outer rotor that are joined at one end with an end section so that a cavity is formed. The stator core is arranged in the cavity in a manner so that the machine has two concentric air gaps between the stator core and rotor when viewed in a section at right angles to the axial direction of the machine.

In one preferred embodiment, the machine according to the invention is designed so that the limiting surface of the stator core that faces towards the end section is convex or partly convex, and the side of the end section that faces the stator core has a concave shape, whereby the concave shape matches the said convex surface. In an alternative embodiment, the machine can be provided with two rotors that are mirror images of themselves. The stator can be provided with several windings. For a person skilled in the art of this technology area, other construction designs of the invention within the scope of the wording of the enclosed claims are clearly apparent.

An rotating electrical machine according to the invention thus has both radial and axial magnetic fluxes and it can be categorised as a combined radial/axial flux machine provided with a combined inner/outer rotor.

The dimensions of the rotating electrical machine according to the invention are determined by a number of factors, e.g. output, the number of poles, frequency as well as the magnetic circuits of the rotor and stator, which are determined by the maximum flux density of the flux carrying material and by other magnetic properties. There are a number of advantages with a machine according to the invention relative to conventional machines with a cylindrical rotor and a corresponding stator. One property of the machine according to the invention is that one of the coil ends of the winding, or both of the coil ends, can be utilised to generate moment through the winding being wound axially along the cylinder and around the end of the hollow cylinder that faces towards the end section. In this way, the material is utilised to its maximum and a high frequency of moment can be obtained. The weight and volume for a given desired effect can therefore be reduced. Compared with an alternating current winding in a conventional machine:

- the coil ends/coil basket can be eliminated so that the production of moment takes place with almost the whole length of the alternating current winding, and thus

- the length of the conductor can be reduced with several tens of percent due to the fact that one does not have coil ends/coil basket

- the copper losses in the alternating current winding can be reduced by the same percentage. Another significant advantage of a machine according to the invention is that, based on the starting point of a machine with a mean air gap diameter equal to the mean air gap diameter of a conventional machines with a cylindrical rotor and stator, the axial length of a machine according to the invention will be about half as long as the conventional machine for the same output. This is related to the fact that for a machine according to the invention, a length of air gap is obtained for a certain axial length that is about equal to double the axial length.

DESCRIPTION OF THE FIGURES

Figure 1 shows a torus machine with a horizontal axle according to the prior art.

Figure 2 shows a perspective illustration of a torus machine according to the prior art.

Figure 3 shows how the magnetic fluxes run in a permanently magnetised torus machine according to the prior art. Figure 4 shows one embodiment of a machine according to the invention.

Figure 5 shows a cross-section of one embodiment of a machine according to the invention.

DESCRIPTION OF AN EMBODIMENT A rotating electrical machine according to Figure 4 represents one preferred embodiment of a machine according to the invention. The machine consists of a stator 21 and a rotor 22 that rotates around a vertically arranged axle 23 enclosed in a casing 24. The stator 21, which is attached to the casing 24, includes a hollow cylinder-shaped stator core 28 of magnetisable material with a ring-shaped cross-section and with a spooled stator winding 27. The stator can be provided with a groove for accommodating the stator winding. The term magnetisable material refers to a material that has a relatively high permeability such as laminated thin sheet metal, fragmented thin sheet metal, amorphous thin sheet metal, metal wire and/or soft magnetised powder or a combination of these.

The rotor 22 includes a rotation body comprising a central part forming an inner rotor 29 and a concentric outer hollow cylinder-shaped part with a ring-shaped cross-section forming an outer rotor 25. The inner rotor 29 is designed so that it can be permanently attached to the axle 23 by a means suitable for the purpose. The outer rotor 25 and inner rotor 29 are preferably extended in an axial direction and each of their respective ends are joined to an end section 32 so that a cavity is formed by outer rotor 25, end section 32, and inner rotor 29. According to the shown embodiment of the invention, the limiting surface of the stator core 28 that faces towards the end section 32 is convex or partly convex, and the inside of the end section 32 has a concave shape, whereby the concave shape matches the said convex surface. The stator core and end part can naturally have other suitable designs. The stator core 28 is arranged in the cavity so that an air gap of essentially even thickness is formed between the stator core with the spooled winding and those parts of the rotor that surround the stator core.

The surfaces of the rotor 22 that face towards the cavity, or at least a part of it, are provided with flux-generating parts in the form of permanent magnets 26, either with or without salient poles. The stator core 28 is wound axially along the inside of the cavity, around the end of the stator core that faces towards the end section 32 and axially along the outside. In this way, both coil ends are utilised and, in addition, the "spine" of the stator contributes to moment formation. An inner and an outer rotor machine that interacts with a stator core in one and the same machine is obtained. The winding around the stator core is executed in an inner and outer air gap and a coil end air gap. One of the coil ends thus contributes with moment formation, while at the other end, all the joining together of the winding takes place (not shown in the Figure).

The actual winding comprises cables with a thinly insulated and transposed copper wire to minimise the eddy currents that are generated in the copper. The flux that is generated by the permanent magnets goes in both radial and axial directions, which is why the powdered material is suitable for not only the core but also the permanent magnets.

The stator winding 27 of the machine can be designed in different ways depending on the actual application. If the machine will be used as a synchronous alternating current machine, the stator winding is normally executed as an alternating current winding with 3 -phases, 2-phases 2 x 3 -phases or with any number of phases. The stator can nevertheless have other forms of winding such stated in WO 97/45919.

With reference to Figure 4, the flux-generating parts of the machine 26 in respect to the rotor can also be designed in different ways depending on the actual application. If the machine will be used as a synchronous machine, the flux-generating parts can comprise only permanent magnets designed with or without salient poles.

Figure 5 shows a cross-section of a machine with two poles and one layer of winding to simplify the drawing. The stator 21 is wound with a stator winding 27 and placed within the cavity of the rotor 25, 29 whereby an inner air gap 30 plus an outer air gap 31 are formed. The surfaces of the rotor 25, 29 that face towards the stator 21 are provided with permanent magnets 26.

Depending on the number of phases, etc., the stator winding 27 can be divided into a number of partial windings with respective outlet and connecting possibilities.

Claims

1. Rotating electrical machine including a stator (21) with a stator core (28) having a hollow cylindrical-shaped part of magnetisable material with a spooled stator winding (27) as well as at least one rotor (22) with flux-generating parts in the form of permanent magnets (26), whereby the rotor (22) includes a rotation body comprising an axially extending inner rotor (29) and a concentric axially extending outer rotor (25) that are joined at one end with an end section (32), whereby the inner rotor, outer rotor and end part form a cavity in which the stator core (28) is arranged so that the machine has two concentric gaps of air between the stator core and rotor when viewed in a section at right angles to the axial direction of the machine, characterised in that the concentric air gaps are united with themselves by means of an air gap essentially running in the radial direction of the machine, whereby one coil end of the machine is accommodated in the said radially extending air gap.

2. Rotating electrical machine according to claim 1, characterised in that the inner rotor (29) is a central part connected to the rotation axle (23) of the machine and that the outer rotor (25) is a concentric hollow cylinder part.

3. Rotating electrical machine according to claim 2. characterised in that the limiting surface of the stator core (28) that faces towards the end section (32) is at least partly convex, and that the surface of end section (32) that faces towards the stator core (28) has a concave shape, whereby the concave shape matches the said convex surface.

4. Rotating electrical machine according to any of the previous claims, characterised in that the stator winding (27) is wound axially along the inside of the hollow cylinder-shaped stator core (28), around the end of the hollow cylinder-shaped part that faces towards said end section (32) and axially along its outside.

5. Rotating electrical machine according to any of the previous claims, characterised in that the surfaces of the rotor (25, 29) that face towards the stator core (28) are at least partially provided with permanent magnets (26).

6. Rotating electrical machine according to any of the previous claims, characterised in that powder material is included in the material of the stator and/or rotor.

7. Rotating electrical machine according to any of the previous claims, characterised in that the winding (27) comprises several thin copper wires transposed and insulated from themselves.