Compact electrical machine

Details Compact electrical machine Compact electrical machine

2003-04-04

2004-09-21

Mullins, Burton (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C290S055000, C310S156010, C310S266000

Reexamination Certificate

active

06794781

ABSTRACT:

The present invention relates to a compact electrical machine. In particular, it relates to the integration within the same volume of a magnetic gearing mechanism and an electrical generator/electrical motor.
FIG. 1
illustrates a wind turbine generator
2
having a housing
12
mounted on support
8
via swivel
10
. The wind turbine generator
2
has a rotor
4
having a plurality of blades mounted on a low speed rotor shaft
16
. A tail vane
6
attached to the housing
12
orients the wind turbine generator
2
in the wind so that the blades of the rotor
4
can drive the low speed rotor shaft
16
at low velocities, typically 60 rpm. The low speed rotor shaft
16
is supported using large bearings
14
. The low speed rotation of the low speed rotor shaft
16
is converted into a high speed rotation of a generator shaft
20
using a mechanical gearbox
18
. The generator shaft
20
, which in this example is rotating at 1800 rpm, drives the electrical generator
22
which produces an electrical output
24
. The use of a gearbox
18
to convert the low speed rotation of low speed rotor shaft
16
to the high speed rotation of the generator shaft
20
is particularly important in applications where an electrical generator
22
of reduced size is required, such as in wind turbine generators
2
.
One problem with the mechanical gearbox
18
, is that it requires maintenance. It has been suggested, in “A novel high-performance magnet gear”, K. Atallah et al, IEEE Transactions on Magnetics, vol. 37, no. 4, pt. 1, pp 2844-6, that if rare-earth magnets are used in a magnetic gearbox, then such a magnetic gearbox could be used as a substitute for the mechanical gearbox
18
.
A cross-section of a magnetic gearbox is illustrated in
FIG. 2. A
high speed rotor shaft
20
of reduced diameter is supported within and coaxial with a cylindrical low speed rotor shaft
16
of larger diameter. The low speed rotor shaft
16
has a large number (P
1
) of permanent magnet pole-pairs
30
on the inner surface of the cylinder. The magnets
30
are attached to the inner surface of the steel low speed rotor shaft
16
and extend parallel to one another along a common axis of rotation
34
for the low speed rotor shaft
16
and the high speed rotor shaft
20
. The magnets
30
are oriented so that the sources and sinks of flux are aligned perpendicularly to the axis
34
. The orientation of the magnets
30
alternates. Every second magnet
30
a
has a source of flux directed towards the axis
34
of the low speed rotor shaft
16
and the adjacent magnets
30
b
have their sinks directed towards the axis
34
of the low speed rotor shaft
16
. The high speed rotor shaft
20
has a smaller number (P
2
) of permanent magnetic pole-pairs
32
attached to its outer surface. The high speed rotor shaft
20
is coaxial with the low speed rotor shaft
16
. The magnets
32
are oriented so that the sources and sinks of flux are aligned perpendicularly to the axis
34
. The orientation of the magnets alternates. Every second magnet
32
a
has a source of flux directed towards the axis
34
of the high speed rotor shaft
20
and the adjacent magnets
32
b
have their sinks directed towards the axis
34
of the high speed rotor shaft
20
. A large number (N) of stationary soft iron pole-pieces
36
are located between the exterior of the high speed rotor shaft
20
and the interior of the low speed rotor shaft
16
between the magnets
32
and
30
. The stationary pole-pieces
36
are located at a fixed distance from the common axis
34
and are evenly distributed about that axis. The gearbox operates by locking one shaft's magnetic field onto a space harmonic of the magnetic field created by the other shaft. The gear ratio is given in the simplest case by G=P
2
÷P
1
when N=P
1
+P
2
. The low speed rotor shaft
16
when driven at a low speed causes the high speed rotor shaft
20
to rotate at a high speed, thus torque is transmitted from one shaft to the other at a fixed gear ratio.
It would be desirable to further improve electric machines which drive or are driven by gears.
According to one aspect of the present invention there is provided, an electrical generator arrangement comprising: a first plurality of permanent magnets collectively producing a spatially variable first magnetic field; a second plurality of permanent magnets arranged to rotate about a first axis; interference means positioned between the first plurality of permanent magnets and the second plurality of permanent magnets to interfere with the first magnetic field; motive means for moving the first plurality of permanent magnets and interference means relative to one another, to produce a second magnetic field for rotating the second plurality of permanent magnets; and a stator having windings arranged to transduce a changing magnetic field produced by the rotation of the second plurality of permanent magnets into electrical energy. According to one embodiment, the magnetic interference means are stationary and the first plurality of permanent magnets are mounted to rotate about the first axis.
According to this aspect of the present invention there is also provided a method of generating electricity comprising the steps of: interfering with a first magnetic field produced by a first plurality of permanent magnets to form beats (regular variations) in the first magnet field; using said beating first magnetic field to rotate a second plurality of permanent magnets; and transducing the time variable magnetic field produced by the rotating second plurality of permanent magnets into electrical energy.
According to another aspect of the present invention there is provided an electrical motor arrangement comprising: a first plurality of permanent magnets collectively producing a spatially variable first magnetic field; a second plurality of permanent magnets arranged to rotate about a first axis; interference means positioned between the first plurality of permanent magnets and the second plurality of permanent magnets to interfere with the first magnetic field and motive means for moving the first plurality of permanent magnets and interference means relative to one another, to produce a second magnetic field for rotating the second plurality of permanent magnets, said motive means comprising a stator having windings for transducing a changing electric field in the windings into the rotation of the first plurality of permanent magnets.
According to this aspect of the present invention there is also provided a method of transducing time varying electrical energy into the rotation of a motor shaft, comprising the steps of: using the time varying electrical energy to rotate a first plurality of permanent magnets; interfering with a first magnetic field produced by the rotating first plurality of permanent magnets to form beats in the first magnet field; and using said beating first magnetic field to rotate a second plurality of permanent magnets attached to the motor shaft.
The first magnetic field preferably varies regularly in space. In the air gap adjacent the second plurality of permanent magnets (without the interference means being present) it preferably has an approximately sinusoidal relationship to the radial angle with a period 2&pgr;/P
1
where the first plurality of permanent magnets comprises P
1
pole-pairs.
The interference means may regularly alternate between soft-ferromagnetic elements and non-ferromagnetic elements. The soft-ferromagnetic elements may be iron pole pieces, preferably of the same size with regular gaps between them such that they are evenly distributed at a fixed radius about the first axis. The first plurality P
1
of permanent magnets and the second plurality of permanent magnets P
2
preferably have a plurality N of pole-pieces located between them such that N=P
1
+P
2
. The relative motion between the first plurality of permanent magnets and the interference means produces beating in the first magnetic field.
Preferably, the first plurality of permanent magnets are att

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