WO2017178911A1

WO2017178911A1 - A rotor for a synchronous machine and synchronous machine comprising said rotor

Info

Publication number: WO2017178911A1
Application number: PCT/IB2017/051729
Authority: WO
Inventors: Adolfo Pace
Original assignee: S.M.E S.P.A.
Priority date: 2016-04-13
Filing date: 2017-03-27
Publication date: 2017-10-19
Also published as: ITUA20162566A1

Abstract

A rotor (1) for a synchronous machine extending along an axis of rotation (3) wherein a cross section of said rotor (1 ) with respect to said axis of rotation (3) comprises a plurality of radial ribs (10) wherein each of them connects two magnetically permeable barriers (6) of the same polar sector (4) extending through the space defined by a magnetic insulation barrier (5) interposed between them. In particular, each radial rib (10) extends along its own axis positioned obliquely with respect to the axis "q" (15) of the relative polar sector (4) and towards the axis "q" (15) starting from the axis of rotation (3) towards the outer perimeter of said polar sector (4).

Description

"A rotor for a synchronous machine and synchronous machine comprising said rotor"

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Technical Field

The present invention relates to a rotor for a synchronous machine and a synchronous machine comprising said rotor.

In particular, the present invention relates to the geometric conformation of the flat disks that form the rotor and, in detail, to the particular conformation of the bridges or radial ribs that connect the barriers or segments with high magnetic permeability (and therefore low magnetic reluctance) between them in order to give structural strength to the disk.

Prior Art

In fact, according to the prior art, synchronous machines comprise an external stator with polar windings so as to define a plurality of offset magnetic poles (according to the type and use of the machine) and an internal rotor which has a corresponding number of poles defined by barriers or magnetically permeable segments (reluctance machine) possibly assisted by permanent magnets inserted in the rotor.

In any case, the rotor is preferably formed by a set of disks placed side-by- side along an axis of rotation of the rotor itself. Preferably, each disk is commonly defined as a "lamina".

Each lamina has a magnetic structure divided into polar sectors wherein each of them has a minimum reluctance direction, also defined as the "d" or direct axis, and a maximum reluctance direction, also defined as the "q" or quadrature axis.

When alternating currents are applied to the cables of the stator windings, a rotating magnetic field is produced and the rotor tends to align the "d" axis of each pole with the corresponding peak of the field generated by the stator so as the perform the rotation of the rotor in a synchronised way. Naturally, the above refers to the operation of the synchronous machine as an "electric motor", but the same structure may be used for the operation of the machine as a "generator" (by rotating the rotor, electric currents are generated at the ends of the stator windings).

As already mentioned above, the prior art envisages each rotor lamina being divided into a plurality of polar sectors defining the number of magnetic poles of the machine, wherein each polar sector has one or more magnetic insulation barriers (preferably air) alternating with one or more magnetically permeable barriers (ferromagnetic material) according to an axis "q" of maximum reluctance of the corresponding polar sector. The axis "d" instead defines the separation line between one polar sector and the other.

Furthermore, to give structural strength to the rotor, a plurality of radial ribs is provided, which connect two magnetically permeable barriers of the same polar sector extending through the space defined by the magnetic insulation barrier interposed between them (figure 1 ). In other words, the radial ribs are made of the same material as the lamina, and connect the magnetically permeable barriers to one another so as to keep them joined during rotation.

An example of such a structure in a reluctance machine is described in document WO2010/102671 in which it is possible to see that the magnetic insulation barriers are defined by the areas "4" and the bridges (fig. 1 ) are positioned parallel to the axis "q".

Likewise, in document US5818140, the bridges "Pi" are aligned with the axis "q" (fig. 5).

However, this known technique has some drawbacks.

A first drawback is connected with the fact that the market currently requires motors with higher and higher rotation speeds which consequently implies a structural adaptation both of the magnetic part and the mechanical part of the rotor. In particular, higher rotation speeds imply an increase in the centrifugal force acting on the bridges and, therefore it is often necessary to increase their thickness so as to prevent internal structural breaks. Figure 2 shows a diagram of the forces acting on a bridge during the rotation of the rotor (the lighter areas are those in which the mechanical stresses are more concentrated).

However, an increase in thickness also implies an increase in the inductance along the axis "d" in the form of dispersed fluids, thus reducing the performance levels of the motor. In fact, the power factor of the machine depends on the ratio between the inductance along the axis "d" and the inductance along the axis "q".

Object of the invention

In this situation, the object of the present invention is to realise a rotor for a synchronous machine that obviates the above-cited drawbacks.

It is in particular an object of the present invention to realise a rotor for a synchronous machine that allows the performance levels of the machine to be optimised so as to have a low inductance of axis "q" with the same maximum rotor rotation speed.

It is further an object of the present invention to realise a rotor for a synchronous machine that allows the thickness of the bridges within the rotor to be reduced to a minimum for having a maximum predetermined rotation speed.

The objects indicated are substantially attained by a rotor for a synchronous machine according to what is described in the appended claims.

Brief description of the figures

Further characteristics and advantages of the present invention will more greatly emerge from the detailed description of some preferred but not exclusive embodiments of a rotor for a synchronous machine illustrated in the appended drawings, in which:

- figure 1 shows, in a schematic front view, a disk of the rotor according ₁ to the prior art;

- figure 2 shows, in a schematic front view, a diagram of the forces acting at a bridge of the disk of the rotor according to the prior art;

- figure 3a shows, in a schematic front view, a portion of a disk of the rotor according to a first embodiment of the present invention;

- figure 3b shows, in a schematic front view, a portion of a disk of the rotor according to a second embodiment of the present invention; and

- figure 4 shows, in a schematic front view, a diagram of the forces acting at a bridge of the disk of the rotor according to the present invention.

Detailed description of some preferred embodiments of the invention

With reference to the figures mentioned, the number 1 generally denotes a rotor for a synchronous machine according to the present invention. In particular, the rotor 1 preferably comprises a plurality of flat disks 2 placed side-by-side along the axis of rotation 3 of the rotor 1 itself for defining the complete rotor 1 . It is to be noted that such disks 2 have the same structural conformation as one another.

Therefore, the cross section of the rotor 1 corresponds to the structure of a disk 2.

In detail, the face of each disk 2 has a plurality of polar sectors 4 defining the number of magnetic poles of the machine into which the rotor 1 is divided. Each polar sector 4 extends radially from the centre of the disk 2 towards a peripheral zone and its extension is a function of the number of magnetic poles of the machine. For example, figure 1 shows a section of rotor 1 with 4 poles in which each polar sector 4 has an angular extension of 90°. However, the present invention can be applied to any number of poles that the rotor 1 has.

Each polar sector 4 is comprised between two direct axes "d" 14 each defining the minimum reluctance direction and containing the quadrature axis "q". The axes "d" 14 and "q" 15 are radial with respect to the axis of rotation 3 of the rotor 1 .

Preferably, the axis "q" 15 is positioned centrally with respect to the polar sector 4. Moreover, from the appended figures it is possible to see that each axis "q" 15 defines an axis of symmetry of the internal structure of the polar sector 4. Each polar sector 4 structurally has one or more magnetic insulation barriers 5 alternating with one or more magnetically permeable barriers 6 according to the axis "q" 15 of maximum reluctance of the corresponding polar sector 4.

In the preferred embodiment, the magnetic insulation barriers 5 are preferably defined by a lack of material, i.e. by air. In other words, the magnetic insulation barriers 5 are empty through spaces afforded on the disk 2.

Preferably, each insulation barrier 5 extends along its own substantially arched direction of extension between two ends positioned at a perimeter zone 7 of the disk 2. The insulation barrier 5 has a central portion 8 which is further away relative to the perimeter zone 7 and closer to the centre of the disk 2.

In the preferred embodiment illustrated, for example, in figures 3a and 3b, each insulation barrier 5 comprises three portions: the central portion 8 further away relative to the perimeter zone 7 and closer to the centre of the disk 2, and two lateral portions 9.

Each lateral portion 9 extends according to an inclined direction relative to the direction of extension of the central portion 8 towards the perimeter zone 7.

The direction of extension of the central portion 8 is substantially transversal (preferably perpendicular) to the axis "q" 15.

As will be better described below, the bridges 10 separate the lateral portions 9 of the central portion 8 of each insulation barrier 5.

The magnetically permeable barriers 6 are instead defined by the material of the disk 2 itself. Usually the disk 2 is made of a ferromagnetic material. Such magnetically permeable barriers 6 are also defined as "permeable segments". In practice, the magnetically permeable barriers 6 define the preferential lanes for the flows of the magnetic fields.

Preferably, each magnetically permeable barrier 6 has the same extension as the insulation barrier 5 adjacent thereto. In other words, each magnetically permeable barrier 6 has a substantially arched extension between two ends positioned at the perimeter zone 7 of the disk 2 and has a central portion 8 further away relative to the perimeter zone 7 and closer to the centre of the disk 2.

Preferably, the insulation barriers 5 and the magnetically permeable barriers 6 are symmetrical with respect to the axis "q" 15 of the relative polar sector 4.

In other words, starting from the centre of the disk 2 and going towards the periphery according to a radial direction, "full" zones (magnetically permeable barriers 6) and "empty" zones (insulation barriers 5) alternate.

In figures 3a and 3b it is possible to see that there are two magnetically permeable barriers 6 alternating with two insulating barriers 5.

At the perimeter zone 7 of the disk 2, there are joining points or segments 1 1 between the magnetically permeable barriers 6 as the insulation barriers 5 extend at such perimeter zone 7 of the disk 2. Therefore, the perimeter zone 7 of the disk 2 is defined by a continuous circular profile of material.

It is also to be noted that the rotor 1 comprises a plurality of radial ribs 10 or bridges 10 wherein each of them connects two magnetically permeable barriers 6 of the same polar sector 4 extending through the space defined by the magnetic insulation barrier 5 interposed between them. In other words, the radial ribs 10 extend according to a direction that goes from the centre towards the periphery of the disk 2.

Each radial rib 10 extends between two opposite ends, one connected to a first magnetically permeable barrier 6 and the other connected to a second magnetically permeable barrier 6 between which an insulation barrier 5 is interposed.

In other words, the radial ribs 10 hold together the parts of magnetically permeable barriers 6 furthest from the perimeter zone 7 to the centre of the disk 2.

It is to be noted that the disk 2 centrally has a "full" zone 16 of magnetically permeable material.

Each of said radial ribs 10 is positioned laterally relative to the axis "q" 1 5 of the polar sector 4 and, preferably, there are at least two radial ribs 10 crossing the same magnetic insulation barrier 5 positioned at the two opposite sides relative to the axis "q" 15 of such polar sector 4.

The radial ribs 10 can be grouped at least in pairs considering a direction that goes from the axis of rotation 3 towards the outer perimeter of said polar sector 4, wherein the ribs 10 of a respective pair are positioned on opposite sides relative to the axis "q".

Even more preferably, the radial ribs 10 positioned at the two opposite sides relative to the axis "q" 15 are symmetrical relative to said axis "q" 15. In accordance with the present invention, each radial rib 10 extends along its own axis 12 positioned obliquely with respect to the axis "q" 15 of the relative polar sector 4 and towards the axis "q" 15 starting from the axis of rotation 3 towards the outer perimeter of said polar sector 4. In other words, each radial rib 10 is inclined towards the axis "q" 15 of the relative polar sector 4 according to a direction away from the centre of the disk 2. In yet other words, the imaginary continuation of the axis 12 of the radial rib 10 crosses the axis "q" 15 in an opposite position to the centre of the disk 2 and, preferably, outside thereof. Figures 3a and 3b indicate the rotation directions according to which the bridges 10 of the prior art (figure 1 ) have been inclined.

Preferably, the axis 12 of the radial bridge 10 is substantially inclined with respect to the axis "q" 15 (closer) by an angle comprised between 5° and 35°.

Furthermore, the radial ribs positioned on a same side as the axis "q" and belonging to different pairs have the axes 12 inclined towards the axis "q" according to different angles to one another considering a direction that goes from the axis of rotation 3 towards the outer perimeter of said polar sector 4.

In a first embodiment illustrated in figure 3a, such axes 12 are inclined according to increasing angles considering a direction that goes from the axis of rotation 3 towards the outer perimeter of said polar sector 4, so that the axes 12 of the ribs 10 closest to the outer perimeter are more inclined relative to the axis "q" than the axes 12 of the ribs 10 closer to the axis of rotation 3 which will instead be more parallel to the axis "q".

In a second embodiment (figure 3b), such axes 12 are inclined according to decreasing angles considering a direction that goes from the axis of rotation 3 towards the outer perimeter of said polar sector 4, so that the axes 12 of the ribs 10 closest to the outer perimeter are more parallel to the axis "q" than the axes 12 of the ribs 10 closer to the axis of rotation 3 which will instead be more inclined relative to the axis "q". Advantageously, this allows the resultant moments acting at the connection ends of the bridges 10 to the magnetically permeable barriers 6 to be minimised, as a function of the distance from the centre. In fact, in the zones closest to the centre, the moment has a higher intensity and would tend to determine a hinge-like opening of the lamina (and therefore the radial ribs must be more inclined to compensate for such tendency), while towards the perimeter of the lamina only the centrifugal force prevails, which would tend to act almost parallel to the axis "q" (and therefore the radial ribs must be less inclined).

Preferably, said axes 12 are inclined according to a decreasing value which is directly proportional to the radius of the circumference centred on the intersection between the axis "q" and the outer perimeter of the disk and passing through the midpoint of the radial rib 10 affected.

In more detail, the angle of inclination of the axis 12 of a radial rib "X" can be calculated as:

Angle i

Angle _ X = . . ' - ^'- ^'■■ χ CireRadiiis_X

CircRadius - where the index "1 " indicates the radial rib and the radius of the most internal circumference to the lamina and the index "X" indicates the radial rib and the radius of the circumference to be calculated. Preferably, a final corrective factor can be added to or subtracted from such formula. Such final corrective factor is preferably comprised between 2% and 25% of Angle_1 , and even more preferably it is +/- 20% of Angle_1 .

5 Furthermore, the maximum and minimum values that determine the range of possible angles comprised between the axis 12 of the radial rib 10 and the axis "q" is a function of the number of poles and, preferably, is inversely proportional thereto. In detail, to determine such maximum and minimum values, the following formulae can be used:

ArtgleValMax =.3-5⁹- x .

l o "

Ang£e¥aiMin · 5^fc x—

where "p" indicates the number of polar pairs.

Each radial rib 10 has its own rectilinear extension along its own axis 12. In particular, the radial ribs 10 are positioned within the edge of the disk 2. It is also to be noted that the axis 12 of the radial rib 10 is substantially 1 5 aligned with the extension direction of the resultant of most of the forces acting at the end of said radial rib 10 and due to the centrifugal force developed during the rotation of the rotor 1 .

It is also to be noted that the radial ribs positioned on a same side as the axis "q" and belonging to different pairs (arranged consecutively 2 0 considering a direction that goes from the axis of rotation 3 towards the outer perimeter of said polar sector 4) have respective axes that are offset from one another moving away from the axis "q".

In other words, by observing figures 3a and 3b, the base of the insulation barrier interposed between a first pair of radial ribs 10 is substantially 2 5 equal to the base of the insulation barrier interposed between the successive pair of radial ribs 10 going towards the outer perimeter.

In yet other words, by observing figures 3a and 3b, the area of the insulation barrier interposed between a first pair of radial ribs 10 is substantially equal to the area of the insulation barrier interposed between the successive pair of radial ribs 10 going towards the outer perimeter. In an alternative embodiment (IPM machine or variable reluctance machine assisted by a magnet) the rotor 1 comprises a plurality of permanent magnets 13 each positioned in a respective polar sector 4 and each having an orientation of its own magnetic field substantially aligned, preferably coinciding, with the axis "q" 15.

Preferably, each of said magnets is positioned in the space within the insulation barrier 5 positioned between two radial ribs 10.

The subject matter of the present invention is also a synchronous machine comprising the rotor 1 previously described. It is to be noted that the machine may have any number of poles.

In particular, such machine is of the IPM (internal permanent magnets) type or synchronous with variable reluctance or synchronous with variable reluctance assisted by a permanent magnet.

In any case, the machine comprises a stator that surrounds the rotor 1 and comprises a plurality of slots as a function of the number of poles for realising the windings of the cables.

The present invention attains the set aims.

In particular, the present invention allows the resultant moments acting at the connection ends of the bridges 10 to the magnetically permeable barriers 6 to be minimised so as to make the structure more resistant even at the higher rotation speeds required by the market.

From a comparison between figure 2 and figure 4, it is possible to observe that the structure with "oblique" bridges 10 according to the present invention allows a better distribution of the traction forces acting on the bridges 10 to be obtained. In fact, in figure 4, the traction forces are better distributed along the actual axis of the bridge 10 where it is stronger. In figure 2 instead, the traction forces were concentrated on the points of contact between the bridge 10 and the magnetically permeable barriers 6 generating a moment. In that way, stresses, concentrations of forces and tensions, particularly at the connection ends of the bridges 10, are consequently minimised.

In addition, it is to be noted that the present invention allows a lower thickness of bridges 10 to be obtained for the same maximum rotation speed with a consequent reduction of the inductance of axis "q" 15 hence increasing the performance levels of the motor.

Also, worthy of note is that the present invention is relatively easy to realise and also that the cost connected to the actuation of the invention is not very high.

Claims

1. A rotor (1 ) for a synchronous machine extending along an axis of rotation (3), wherein a cross section of said rotor (1 ) relative to said axis of rotation (3) comprises:

- a plurality of polar sectors (4) defining the number of magnetic poles of the machine into which the rotor (1 ) is divided, wherein each polar sector (4) has at least two magnetic insulation barriers (5) alternating with respective magnetically permeable barriers (6) according to an axis "q" (15) of maximum reluctance of the corresponding polar sector (4);

- a plurality of radial ribs (10) wherein each of them connects two magnetically permeable barriers (6) of a same polar sector (4) extending through the space defined by the magnetic insulation barrier (5) interposed between them; each of said radial ribs (10) being positioned laterally with respect to the axis "q" (15) of the polar sector (4); said radial ribs (10) being grouped at least in pairs considering a direction that goes from the axis of rotation (3) towards the outer perimeter of said polar sector (4), wherein the ribs (10) of a respective pair are positioned on opposite sides relative to the axis "q";

- each radial rib (10) extends along its own axis (12) positioned obliquely with respect to the axis "q" (15) of the relative polar sector (4) wherein said axis (12) is inclined towards the axis "q" (15) by an angle comprised between and maximum value and a minimum value, considering a direction that goes from the axis of rotation (3) towards the outer perimeter of said polar sector (4);

characterised in that each of the maximum and minimum values is a function of the number of poles and, preferably, is inversely proportional thereto; said radial ribs positioned on a same side relative to the axis "q" and belonging to different pairs, having axes (12) inclined towards the axis "q" according to different angles to one another considering a direction that goes from the axis of rotation (3) towards the outer perimeter of said polar sector (4).

2. The rotor (1 ) according to claim 1 characterised in that said axes (12) inclined towards the axis "q" according to different angles to one another, are inclined according to decreasing angles considering a direction that goes from the axis of rotation (3) towards the outer perimeter of said polar sector (4), so that the axes (12) of the ribs (10) closest to the outer perimeter are more parallel to the axis "q" than the axes (12) of the ribs (10) closer to the axis of rotation (3).

3. The rotor according to claim 2 characterised in that said axes (12) are inclined according to a decreasing value which is directly proportional to the radius of the circumference centred on the intersection between the axis "q" a^ncl the ^outer perimeter of the disk and passing through the midpoint of the radial rib (10) affected.

4. The rotor (1 ) according to claim 1 characterised in that said axes (12) inclined towards the axis "q" according to different angles to one another, are inclined according to increasing angles considering a direction that goes from the axis of rotation (3) towards the outer perimeter of said polar sector (4), so that the axes (12) of the ribs (10) closest to the outer perimeter are more inclined relative to the axis "q" than the axes (12) of the ribs (10) closer to the axis of rotation (3).

5. The rotor according to any one of the preceding claims characterised in that the radial ribs positioned on a same side as the axis "q" and belonging to different pairs have respective axes that are offset from one another moving away from the axis "q" considering a direction that goes from the axis of rotation (3) towards the outer perimeter of said polar sector (4)

6. The rotor (1 ) according to any one of the preceding claims, characterised in that the axis (12) of the radial rib (10) is substantially aligned with the direction of extension of the resultant of most of the forces acting at the ends of said radial rib (10) and due to the centrifugal force developed during the rotation of the rotor (1 ).

7. The rotor (1 ) according to any one of the preceding claims, characterised in that the axis (12) of the radial rib (10) is substantially inclined by an angle comprised between 5° and 35° relative to the axis "q"

5 (15).

8. The rotor (1 ) according to any one of the preceding claims, characterised in that said maximum value is determined at least by duplicating the value of 35° and dividing it by the number of polar pairs of the rotor (1 ); said minimum value being determined at least by duplicating o the value of 5° and dividing it by the number of polar pairs of the rotor (1 ).

9. The rotor (1 ) according to any one of the preceding claims, characterised in that the radial ribs (10) positioned at the two opposite sides relative to the axis "q" (15) are symmetrical relative to the axis "q" (15).

5 10. The rotor (1 ) according to any one of the preceding claims, characterised in that the rotor (1 ) comprises a perimeter zone (7) defining the contour of the cross section and comprising a plurality of joining points positioned at the ends of the insulation barrier (5).

11. The rotor (1 ) according to claim 10, characterised in that each 0 insulation barrier (5) has a substantially arched direction of extension between two ends positioned at the joining points of the perimeter zone (7); said insulation barrier (5) having a central portion (8) which is further away relative to the perimeter zone (7).

12. The rotor (1 ) according to any one of the preceding claims, 5 characterised in that said rotor (1 ) comprises a plurality of flat disks (2) placed side-by-side along the axis of rotation (3); each of said disks (2) being shaped like said cross section.

13. The rotor (1 ) according to any one of the preceding claims, characterised in that it comprises a plurality of permanent magnets (13),0 each positioned in a respective polar sector (4) and each having an orientation of its magnetic field which is substantially aligned with the axis "q" (15).

14. The rotor (1 ) according to claim 13, characterised in that each of said magnets is positioned in the space within the insulation barrier (5) positioned between two radial ribs (10).

15. A synchronous machine comprising a rotor (1 ) according to any one of the preceding claims, characterised in that said machine is of the IPM type or variable reluctance synchronous or variable reluctance synchronous assisted by permanent magnet.