SYNCHRONOUS RELUCTANCE MACHINE

Abstract

The present invention relates to electrical engineering, particularly to synchronous reluctance machines, and can be used in electrical drives for machines and mechanisms, as well as in electrical power generators. The synchronous reluctance machine comprises a stator with a winding arranged within stator slots, and a rotor mounted to provide a gap between the rotor and the stator, the rotor being rotatable with respect to the stator and comprising radially alternating magnetically permeable layers and flux barriers, wherein each barrier comprises at least one peripheral end extending towards the circumferential rotor surface and the angular pitch of the peripheral ends decreases in circumferential direction from the peripheral ends of the outer barriers towards the peripheral ends of the deepest inner barriers among at least three circumferentially sequential peripheral ends, wherein at least two of said ends are inner barrier ends. This results in improved energy characteristics of the reluctance machine, in particular power factor, efficiency and specific power thereof, for the same number of flux barriers. This is further achieved by a synchronous reluctance machine comprising a stator with a winding arranged within stator slots, and a rotor mounted to provide a gap between the rotor and the stator, the rotor being rotatable with respect to the stator and comprising radially alternating magnetically permeable layers and flux barriers, the gap is increased by 15-400% between the surface of the most external magnetically permeable layer and the stator compared to other sections of the gap.

Claims

1. A synchronous reluctance machine comprising: a stator with a winding arranged within stator slots, a rotor mounted to provide a gap between the rotor and the stator, the rotor being rotatable with respect to the stator and comprising radially alternating magnetically permeable layers and flux barriers, wherein each barrier comprises at least one peripheral end extending towards the circumferential rotor surface, wherein the angular pitch of the peripheral ends decreases in circumferential direction from the peripheral ends of the outer barriers towards the peripheral ends of the deepest inner barriers among at least three circumferentially sequential peripheral ends, and wherein at least two of said ends are inner barrier ends.

2. The machine according to claim 1, wherein for any sequence of n+1 angular pitches, where n2, the sequence including the angular pitch (.sub.0) defined by the peripheral ends of the two deepest inner barriers, the closest angular pitch (.sub.n) thereto being defined by the peripheral ends of at least one outer barrier, and all circumferentially sequential angular pitches therebetween, from .sub.1 to .sub.n1, where .sub.1 is the pitch immediately following pitch .sub.0, and .sub.n-1 is the pitch immediately preceding pitch .sub.n, the following is true for at least one pair of sequential angular pitches:
.sub.m1<.sub.m, where 0<m<n.

3. The machine according to claim 1, wherein for any sequence of n+1 angular pitches, where m2, the sequence including the angular pitch (.sub.0) defined by the peripheral ends of the two deepest inner barriers, the closest angular pitch (.sub.n) thereto being defined by the peripheral ends of at least one outer barrier, and all circumferentially sequential angular pitches therebetween, from .sub.1 to .sub.n1, where .sub.1 is the pitch immediately following pitch a.sub.0, and .sub.n1 is the pitch immediately preceding pitch .sub.n. the following is true:
.sub.0<.sub.1 and .sub.0.sub.2.

4. The machine according to claim 1, wherein for the angular pitch (.sub.0) defined by the peripheral ends of the two deepest inner barriers and for the closest angular pitch (.sub.1) thereto, the following is true:
.sub.0<.sub.1.

5. The machine according to claim 1, wherein for any sequence of n+1 angular pitches, where n2, the sequence including the angular pitch (.sub.0) defined by the peripheral ends of the two deepest inner barriers, the closest angular pitch (.sub.n) thereto being defined by the peripheral ends of at least one outer barrier, and all circumferentially sequential angular pitches therebetween, from .sub.1 to .sub.n1, where .sub.1 is the pitch immediately following pitch .sub.0, and .sub.n1 is the pitch immediately preceding pitch .sub.n, the following is true:
.sub.m1<.sub.m, where 0<mn.

6. The machine according to claim 1, wherein magnetically permeable layers are connected via inner and/or peripheral links, wherein peripheral links separate peripheral ends of barriers from the gap.

7. The machine according to claim 1, wherein the flux barriers reach the gap, and the angular pitch is defined as the angular distance between pitch points which are midpoints of outer circumference arcs of the transverse projection of the rotor, the arcs separating circumferentially adjacent magnetically permeable layers.

8. The machine according to claim 1, wherein peripheral ends of the flux barriers are separated from the gap by a peripheral link, and the angular pitch is defined as the angular distance between pitch points located on the circumference of the cross-section of the rotor, the pitch points corresponding to the midpoint of a link section of minimum thickness in the direction of the gap.

9. The machine according to claim 1, wherein the peripheral ends of the flux barriers are separated from the gap by a peripheral link, and the angular pitch is defined as the angular distance between pitch points located on the circumference of the cross-section of the rotor, the pitch points corresponding to the midpoint of a link section having a thickness in the direction of the gap differing by no more than 5% from the minimum link thickness in the direction of the gap.

10. The machine according to claim 1, wherein the peripheral ends of the flux barriers are separated from the gap by a peripheral link, and the angular pitch is defined as the angular distance between pitch points located on the circumference of the cross-section of the rotor, the pitch points corresponding to the midpoint of a link section having a thickness in the direction of the gap differing by no more than 20% from the minimum link thickness in the direction of the gap.

11. The machine according to claim 1, wherein the winding is concentrated.

12. The machine according to claim 1, wherein the winding is distributed.

13. The machine according to claim 1, wherein the rotor comprises sheets with transverse lamination.

14. The machine according to claim 1, wherein the rotor comprises sheets with longitudinal lamination.

15. The machine according to claim 1, wherein at least one of the flux barriers comprises a permanent magnet or several permanent magnets.

16. The machine according to claim 1, wherein the gap is increased between the surface of the most external magnetically permeable layer and the stator compared to other sections of the gap.

17. A synchronous reluctance machine comprising: a stator with a winding arranged within stator slots, a rotor mounted to provide a gap between the rotor and the stator, the rotor being rotatable with respect to the stator and comprising radially alternating magnetically permeable layers and flux barriers, wherein the gap is increased by 15-400% between the surface of the most external magnetically permeable layer and the stator compared to other sections of the gap.

18. The machine according to claim 17, wherein the gap is increased by 15-200% between the surface of the most external magnetically permeable layer and the stator compared to other sections of the gap.

19. The machine according to claim 17, wherein at least one flux barrier comprises a permanent magnet or several permanent magnets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described in the context of specific embodiments with reference to the accompanying drawings, wherein:

[0029] FIG. 1 illustrates a rotor structure according to an embodiment;

[0030] FIG. 2 schematically illustrates distribution of magnetic flux paths according to one embodiment;

[0031] FIG. 3 schematically illustrates the process of selecting pitch angles;

[0032] FIG. 4 illustrates a rotor structure comprising cutouts according to one embodiment;

[0033] FIGS. 5 and 6 illustrate a rotor structure comprising magnets according to one embodiment.

[0034] FIGS. 7 and 8 illustrate a rotor structure comprising cutouts and magnets according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The embodiments of the disclosed synchronous reluctance machine (SynRM) are aimed at increasing its energy characteristics (efficiency, specific torque and specific power) for a fixed number of flux barriers.

[0036] In one embodiment, the SynRM comprises a stator with a winding arranged within stator slots, and a rotor mounted to provide a gap between the rotor and the stator, the rotor being rotatable with respect to the stator. Stator winding can be distributed or concentrated.

[0037] FIG. 1 illustrates a rotor structure. In one embodiment, the rotor is a steel cylinder comprised of sheets with transverse lamination. The rotor comprises alternatingly arranged magnetically permeable layers 1 (i.e., layers of high magnetic permeability) and flux barriers 2, 8 and 9 (i.e., layers of low magnetic permeability). Axis 4 of high magnetic permeability is defined as the d-axis, and axis 5 of low magnetic permeability is defined as the q-axis. The flux barriers 2, 8 and 9 are formed by cutting longitudinal slits in the sheets. The flux barriers 2, 8 and 9 each have an elongated shape and comprise barrier ends. The barrier ends extending towards the circumferential rotor surface are referred to as peripheral barrier ends 13, and the barrier ends extending into the rotor are referred to as inner barrier ends 14. The barrier 2 has one peripheral barrier end and one inner barrier end, whereas the barriers 8 and 9 each have two peripheral barrier ends. Rotor integrity is provided by thin links connecting the magnetically permeable layers 1. Links arranged on the rotor circumference are referred to as peripheral links 6, while the remaining links are referred to as inner links 7. The peripheral links 6 separate the peripheral barrier ends from the gap. The inner links separate individual barriers from each other. The rotor is arranged on a shaft 3. In another embodiment, the rotor is formed as a steel cylinder comprised of sheets with longitudinal lamination. In this case, the flux barriers 2, 8 and 9 reach or extend up to the air gap.

[0038] FIGS. 5 and 6 illustrate a rotor structure according to one embodiment with permanent magnets 11 mounted into one or more flux barriers 12. In some embodiments, the permanent magnets can be mounted into all flux barriers 12. The permanent magnets 11 take up a portion of the flux barrier 12. As shown in FIG. 8, the rotor comprises the inner links 7 providing more accurate positioning of the permanent magnets 11 to alleviate rotor imbalance. The links 7 further provide mechanical stability for the rotor. In another one embodiment, the permanent magnets 11 can take up the entirety of one or more flux barriers.

[0039] Further description requires explanation of the term pitch point.

[0040] When the barriers reach the gap, the pitch point is the midpoint of the outer circumference arc of the transverse projection of the rotor, said arc separating circumferentially adjacent magnetically permeable layers, and when peripheral ends of the barriers are separated from the gap by a peripheral link, the pitch point is located on the circumference of the cross-section of the rotor and corresponds to the midpoint of a link section of minimum thickness in the direction of the gap. The angular distance between adjacent pitch points defines the angular pitch of the peripheral ends of flux barriers.

[0041] In another one embodiment, when peripheral ends of the flux barriers are separated from the gap by a peripheral link, the pitch point is located on the circumference of the cross-section of the rotor and corresponds to the midpoint of a link section having a thickness in radial direction differing by no more than 20%, preferably by no more than 5%, from the minimum link thickness in the direction of the gap.

[0042] The alternating current passing along stator windings forms a rotating magnetic field in the air gap. Rotational torque is formed due to the fact that the rotor strives to position the rotor axis 4 of high magnetic permeability (d-axis) in such manner with respect to the magnetic field as to minimize magnetic reluctance in the magnetic circuit.

[0043] FIG. 2 schematically illustrates the q-axis magnetic flux path. A portion of the q-axis magnetic flux (macroscopic flux a) travels in a transverse direction with respect to the flux barriers. Another portion of the q-axis magnetic flux (microscopic flux b) travels over the magnetically permeable layers between adjacent pitch points due to the finite thickness of the magnetically permeable layers. The present invention is aimed at decreasing the q-axis magnetic flux and therefore increasing magnetic anisotropy due to a decrease in the microscopic component.

[0044] Upon excitation of the q-axis flux, the absolute maximum value of magnetic differences of potential (MDP) is created on the q-axis. Conversely, a decrease in MDP at arc sections with identical angular size is minimal in proximity of the q-axis and increases in the direction of the d-axis. The closer to the d-axis (and the further from the q-axis), the smaller angular pitch should be selected.

[0045] An example of selecting angular pitch ratios for three flux barriers per pole is illustrated in FIG. 3.

[0046] When n=3, angular pitches are selected using the following formula:

.sub.m1<.sub.m, where 0<mn, (1)

where [0047] .sub.m is a pitch in the direction away from the d-axis; [0048] .sub.0 is the angular size of the pitch enclosing the d-axis; and [0049] .sub.n is the angular pitch enclosing the q-axis.

[0050] Each pitch encloses one area of high magnetic permeability. As seen in FIG. 3, the following inequations are true for the angular pitches: .sub.0<.sub.1, .sub.1<.sub.2 and .sub.2<.sub.3.

[0051] Although in the above example with reference to FIG. 3 the ratio of angular pitches am is shown and described for one section of the arc between q-axis and d-axis, it should be noted that the same ratio of angular pitches am is also typical for other sections of the arc between q-axis and d-axis.

[0052] The number (n) of flux barriers per pole is not necessarily 3 and can be a different number.

[0053] In use, the present invention provides a decrease in microscopic stray flux and, consequentially, an increase in power factor, efficiency, specific torque and specific power.

[0054] Due to factors specific to designing SynRMs outside the scope, particularly due to strength calculation or heat calculation requirements, a compromise may be necessary, wherein the inequation (1) is partially untrue. Therefore, in some embodiments, the principle of selecting the angular pitch to be smaller in the direction away from q-axis (and therefore, towards the d-axis) in order to increase the magnetic anisotropy of the rotor can be partially implemented through other ratios between the angular pitches of pitch points.

[0055] In particular, in one embodiment, the angular pitches are selected in accordance with the following formula:

.sub.m1<.sub.m, where 0<m<n, (2)

wherein the inequation is true for at least one pair of sequential angular pitches.

[0056] In another one embodiment, for a sequence of 4 angular pitches including the angular pitch .sub.0 defined by the peripheral ends of two inner barriers 2, the angular pitch .sub.3 closest thereto and defined by the peripheral ends of the outer barrier 9, and all angular pitches .sub.1-.sub.2, the following is true:

.sub.0<.sub.1 and .sub.0.sub.2. (3)

[0057] In another one embodiment, for the angular pitch .sub.0 defined by the peripheral ends of the two deepest inner barriers 2 and for the closest angular pitch thereto (.sub.1), the following is true:

.sub.0<.sub.1. (4)

[0058] It should be noted that although in some embodiments, the angular pitch of the peripheral ends of flux barriers is determined as the angular distance between pitch points, in other embodiments, said angular pitch can be determined using any suitable method.

[0059] In yet another embodiment shown in FIG. 4, the rotor comprises a cutout 10 in the proximity of the q-axis. The deviations from the cylindrical shape of the rotor increase magnetic anisotropy and decrease magnetic flux leakage in the higher harmonics of the stator, thus increasing energy characteristics of the machine (efficiency, power factor) and increasing its specific characteristics (specific torque and specific power).

[0060] In yet another embodiment, the gap between the outer magnetically permeable layer and the stator is increased by 15-400%, preferably by 15-200%, compared to other sections of the gap due to said cutout 10. Small deviations from the cylindrical shape of the rotor allow it to retain excellent hydrodynamic characteristics, eliminate magnetic flux leakage and the q-axis flux, increase magnetic anisotropy, and only marginally impede flux path on the d-axis, thus further increasing energy characteristics of the machine (efficiency, power factor) and increasing its specific characteristics (specific torque and specific power).

[0061] FIGS. 7 and 8 illustrate a rotor structure with cutouts according to one embodiment of the invention, with permanent magnets 11 mounted into one or more flux barriers 12. In some embodiments, the permanent magnets can be mounted into all flux barriers 12. The permanent magnets 11 take up a portion of the flux barrier 12. As can be seen in FIG. 9, the rotor comprises inner links 7 providing more accurate positioning of permanent magnets 11 to alleviate rotor imbalance. The links 7 further provide mechanical stability for the rotor. In another one embodiment, the permanent magnets 11 can take up the entirety of one or more flux barriers, or of all flux barriers.

[0062] The cutout does not affect the above-described pitch angle ratios or link positioning, and therefore formulae (1), (2), (3) and (4) are true for the present SynRM with cutouts.

[0063] However, in other embodiments, said cutouts can also be used in SynRMs wherein the angular pitch is not selected to be smaller in the direction towards the d-axis and further away from the q-axis, particularly wherein formulae (1), (2), (3) and (4) are not true, but wherein an increase in energy characteristics of the machine (efficiency, power factor) and its specific characteristics (specific torque and specific power) is still achieved.

[0064] It should be noted that in the foregoing description, the disclosure of properties or features of the synchronous reluctance machine in the context of a section of the rotor arc and/or d-axis area and/or q-axis area is should be interpreted as encompassing all analogous sections of the rotor arc and/or d-axis areas and/or q-axis areas.

[0065] The embodiments described above are provided as non-limiting examples and should not be construed as limiting the spirit and scope defined by the accompanying claims.