SE1651722A1 - Electrical rotating machine with an inner stator, outer stator and a rotor comprising magnet sets - Google Patents

Description

15 20 25 The machine of DE19753916 risks producing high eddy currents in the magnets of the rotor, which increases losses and heat. Moreover, manufacturing of the electrical machine should be simplified.

SUMMARY It is an object to provide an electrical rotating machine where eddy currents are reduced.

According to a first aspect, it is presented an electrical rotating machine comprising: an inner stator; an outer stator; and a rotor provided radially between inner stator and the outer stator, wherein the rotor comprises a main rotor body, the main rotor body extending for a majority of the rotor in a radial direction and the main rotor body comprising magnet sets and non- magnetic supports provided between each pair of adjacent magnet sets in a circumferential direction; wherein each magnet set passes through the main rotor body in a radial direction, and each one of the magnet sets comprises a plurality of separate magnets in an axial direction.

The rotor may consist of the main body.

The rotor may comprise an inner sheet radially inside of the main body and an outer sheet radially outside the main body.

The inner sheet may be non-magnetic and the outer sheet may be non- magnetic The inner sheet may be magnetic and the outer sheet may be magnetic Electrically insulating material may be provided between the magnets of each magnet set.

The magnets of each magnet set may be aligned in a circumferential direction and in a radial direction.

The magnetic poles of all magnets may be aligned within each magnet set. 10 15 20 25 The magnets may be provided, circumferentially, with radially alternating pole directions.

The electrical rotating machine may further comprise a drive shaft, and a connecting structure between the rotor and the drive shaft, wherein the inner stator is provided only on one side of the connecting structure.

The outer stator may also be provided on the same side of the connecting StfllCtllfe EIS thê lIIIIGI' StatOf.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/ an/ the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a schematic diagram illustrating an electrical rotating machine, used to illustrate directional terms used herein; Fig 2 is a schematic diagram of a rotating electrical machine being a double stator machine; Fig 3 is a schematic diagram illustrating a section of the electrical rotating machine of Fig 2 in more detail; Fig 4 is a schematic perspective view of the rotor of Fig 3 according to one embodiment; Fig 5 is a schematic diagram illustrating a section of the electrical rotating machine of Fig 2 in more detail when inner and outer sheets are provided as part of the rotor; and 10 15 20 25 30 Fig 6 is a schematic side view of the electrical rotating machine of Fig 2 according to one embodiment.

DETAILED DESCRIPTION The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig 1 is a schematic diagram illustrating an electrical rotating machine 10, used to illustrate directional terms used herein.

The electric rotating machine 10 can function as a generator or a motor.

Rotation in the electric rotating machine 10 occurs around an axis 88, defining an axial direction 90. A cross-sectional plane 91 is an imaginary (which can coincide with a real) plane perpendicular to the axis 88. A direction, in a cross-sectional plane 91 from the axis 88 outwards, is denoted a radial direction 93. A (curved) direction in a cross-sectional plane 91 at a constant radial distance from the axis 88 is denoted a circumferential direction 92. In any one point on the cross-sectional plane 91, the circumferential direction 92 is perpendicular to the radial direction 93. The circumferential direction 92 is positive in a clockwise direction.

Fig 2 is a schematic diagram of a rotating electrical machine being a double stator machine. There is here an inner stator 2 and an outer stator 1. A rotor 3 is provided radially between the inner stator 2 and the outer stator 1. An inner air gap 8a is provided between the inner stator 2 and the rotor 3. An outer air gap 8b is provided between the outer stator 1 and the rotor 3.

The rotor 3 rotates in the air gaps between the two stators 1, 2. The rotor comprises magnets. Since there are two air gaps 8a-b, torque is produced in 10 15 20 25 30 both air gaps, which significantly increases the torque and power density in comparison to traditional electrical rotating machines with a single air gap.

Fig 3 is a schematic diagram illustrating a section of the electrical rotating machine 10 of Fig 2 in more detail. In the embodiment of Fig 3, the rotor 3 consists of a main body 11, without any additional elements. The main body 11 comprises magnet sets 5, passing completely through the main body 11 in a radial direction 93. Non-magnetic supports 4 are provided between adj acent magnet sets 5 in a circumferential direction 92. The supports 4 hold the magnets 5 in place in the main body 11.

The arrow inside each magnet set 5 shown in Fig 3 indicates the direction of a magnetic flux through the magnet set 5. In other words, the arrow is pointing in a direction from the south pole of each magnet set to the north pole of each magnet set.

Both the outer stator 1 and the inner stator 2 comprise stator teeth allowing coils to be provided around the stator teeth. A magnetic flux 15 is shown which loops from the outer stator 1, radially inwards through one magnet set 5, to the inner stator 2, passing through the inner stator 2 in a reverse circumferential direction 92 and radially outwards through another magnet set 5 back to the outer stator 1. It is to be noted that the magnetic flux 15 shown here is only an example. Magnetic fluxes may also exist that pass through more stator teeth. Additionally, each magnet set 5 can cover any suitable number of stator teeth, i.e. fewer or more than what is shown in Fig 3.

The magnet sets 5 are provided, circumferentially, with radially alternating pole directions. This enables a circular magnetic flux 15. The magnet sets 5 can be magnetized in the radial direction, or in a parallel direction, whereby the magnetic flux generated by each magnet set alone is in a single direction within the respective magnet set. When magnetized in a parallel direction, the direction of magnetization is aligned with a radial direction for at least one part of the magnet set 5, e.g. in the middle of the magnet set 5. When the 10 15 20 25 radius is large compared to the circumferential length of the magnet set, the parallel direction is essentially the same as the radial direction.

The supports 4 can e.g. be made by aluminium or non-magnetic steel. When the supports 4 are made of non-magnetic steel or a non-magnetic metallic alloy, the leakage flux between the magnet sets 5 in the rotor 3 is drastically reduced, which leads to an increased machine efficiency.

In the prior art, the rotor can have permanent magnets provided (on the surface or inset) on either side of the rotor radially, with another material provided between the permanent magnets. Compared to the surface mounted or inset permanent magnet configuration in the rotor, the rotor presented here can be made thinner. When the rotor 11 is thinner, the diameter of the inner air gap 8a can be increased for a given outer dimension, which thus produces a higher torque density.

The shape of the sides of the magnet sets 5, in the circumferential direction towards the supports, might be round or in any other suitable form for easier manufacturing and/ or increased mechanical strength in attachment to the supports 4.

There are the same number of stator cores in the outer stator 1 and the inner stator 2. The stator cores of the outer stator 1 and the inner stator 1 are aligned in the circumferential direction 92. Additionally, the permanent magnets are shaped for each air gap. In this way, it is possible to reduce the rotor torque ripple by mutual/reciprocal cancelling of harmonics in each air gap.

The rotating electrical machine presented in embodiments herein can be applied for any suitable purpose, e.g. large machines in wind generators and marine propulsion, smaller electrical motors as in automotive traction applications and industrial machines, etc.

In wind power applications, the higher power density leads to a smaller nacelle size for a given power rating, which simplifies the mechanical tower 10 15 20 25 30 and nacelle construction. In marine propulsion a reduction in volume reduces the drag in the water.

Another advantage of the double stator machine is better fault tolerance with respect to inverter or winding failure in one stator. Under these conditions it is possible to continue the operation at reduced power (using the other stator) until maintenance occurs. This is especially important for off-shore wind power or marine propulsion where a continued operation is very important and a quick service response is not always possible.

Fig 4 is a schematic perspective view of the rotor 3 of Fig 3 according to one embodiment. By showing the structure of one magnet set along the axial direction, it is here seen illustrated that each one of the magnet sets 5 in the rotor comprises a plurality of separate magnets 9a-c in the axial direction 90.

Specifically, the magnet set 5 shown here comprises a first magnet 9a, a second magnet 9b and a third magnet 9c. The number of magnets can vary depending on the implementation as long as there are at least two magnets in each magnet set. Each magnet 9a-c can be a permanent magnet. For instance, each magnet 9a-c can be a ferrite magnet or a rare earth permanent magnet, such as neodymium-iron-boron, or samarium-cobalt.

The magnets 9a-c of each magnet set 5 are aligned in a circumferential direction and in a radial direction. Also, the magnetic poles of all magnets 9a- c are aligned within each magnet set.

By providing separate magnets in the axial direction, manufacturing is made more efficient. Electrically insulating material is optionally provided between the magnets 9a-c of each magnet set. This reduces eddy current losses, since the size of a possible eddy current loop is reduced when the size of each single magnet 9a-c is reduced. This is particularly applicable when the magnets 9a-c are rare earth permanent magnets, which often have high electric conductivity. Furthermore, the permanent magnets of a magnet set can also be divided in several parts in the radial direction for an easier production and manufacturing. 10 15 20 25 Fig 5 is a schematic diagram illustrating a section of the electrical rotating machine 10 of Fig 2 in more detail when inner and outer sheets are provided as part of the rotor 3.

Here, the rotor 3 comprises an inner sheet 7a radially inside of the main body 11 and an outer sheet 7b radially outside the main body 11. The sheets 8a-b provide improved stability for the rotor 3.

In one embodiment, the inner sheet 7a is magnetic and the outer sheet is magnetic. This reduces the magnetic reluctance in a radial direction between the stators 1, 2 and the rotor. However, when the sheets 7a-b are magnetic, there is more flux leakage in a circumferential direction.

In one embodiment, the inner sheet 7a is non-magnetic and the outer sheet is non-magnetic. This reduces flux leakage in a circumferential direction.

However, the non-magnetic implies a greater magnetic reluctance in a radial direction between the stators 1, 2 and the rotor. The sheets can e.g. be made of metal, carbon fibre, or other strong material which provides sufficient support for the rotor.

The selection of either magnetic or non-magnetic material for the sheets 7a, 7b thus depends on the application.

Fig 6 is a schematic side view of the electrical rotating machine 10 of Fig 2 according to one embodiment. Here, a centrally located drive shaft 12 can be seen. A connecting structure 13 is provided between the rotor 3 and the drive shaft 12.

The inner stator 2 is provided only on one side of the connecting structure 13.

In this way, manufacturing is made easier for the stators 1, 2. The stators 1, 2 can easily be fixedly connected on the opposite end from the connecting structure 13. The connecting structure 13, in turn, fixedly connects the rotor 3 and the drive shaft 12, e.g. using a disc or spokes. Additionally, the rotor 3 can be fixedly connected to the shaft 12 using the connecting structure on its end. Optionally, both the inner stator 2 and the outer stator 1 are both 10 provided only on one side of the connecting structure 13.Also, the windings of the outer stator 1 and the inner stator 2 are all provided sequentially in the axial direction, without being interrupted by any connecting structure between rotor and drive shaft which would introduce additional end windings. End windings are less power efficient than intermediate windings.

Hence, a machine with fewer end windings produces more power than a machine with more end windings of the same volume.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims (11)

10 15 20 25 10 CLAIMS

1. An electrical rotating machine (10) comprising: an inner stator (2); an outer stator (1); and a rotor (3) provided radially between the inner stator (2) and the outer stator (1), wherein the rotor comprises a main rotor body, the main rotor body extending for a majority of the rotor in a radial direction and the main rotor body comprising magnet sets (5) and non-magnetic supports provided between each pair of adj acent magnet sets (5) in a circumferential direction; wherein each magnet set (5) passes through the main rotor body in a radial direction, and each one of the magnet sets (5) comprises a plurality of separate magnets (9a-c) in an axial direction (90).

2. The electrical rotating machine (10) according to claim 1, wherein the rotor (3) consists of the main body.

3. The electrical rotating machine (10) according to claim 1, wherein the rotor (3) comprises an inner sheet (7a) radially inside of the main body and an outer sheet (7b) radially outside the main body.

4. The electrical rotating machine (10) according to claim 3, wherein the inner sheet (7a) is non-magnetic and the outer sheet (7b) is non-magnetic

5. The electrical rotating machine (10) according to claim 3, wherein the inner sheet (7a) is magnetic and the outer sheet (7b) is magnetic

6. The electrical rotating machine (10) according to any one of the preceding claims, wherein electrically insulating material is provided between the magnets (9a-c) of each magnet set.

7. The electrical rotating machine (10) according to any one of the preceding claims, wherein the magnets of each magnet set are aligned in a circumferential direction and in a radial direction. 10 15 11

8. The electrical rotating machine (10) according to any one of the preceding claims, wherein the magnetic poles of all magnets (9a-c) are aligned within each magnet set.

9. The electrical rotating machine (10) according to any one of the preceding claims, wherein the magnet sets (5) are provided, circumferentially, With radially alternating pole directions.

10. The electrical rotating machine (10) according to any one of the preceding claims, further comprising a drive shaft (12), and a connecting structure (13) between the rotor (3) and the drive shaft (12), wherein the inner stator (2) is provided only on one side of the connecting structure (13).

11. The electrical rotating machine (10) according to any one of the preceding claims, wherein the outer stator (1) is provided on the same side of the connecting structure (13) as the inner stator.