This disclosure relates to the field of synchronous machines, in particular to the field of cogging torque reduction in synchronous machines, and more in particular to the field of cogging torque reduction in synchronous reluctance machines.
Synchronous machines are generally known. In a synchronous reluctance machine, generally, there is a stator with multiphase windings forming a plurality of poles which are similar to those of induction motors. The synchronous reluctance machine also includes a rotor that does not use windings but does have the same number of poles as the stator. By providing a rotating field in the stator windings, a magnetomotive force acts upon the rotor resulting in the rotor being driven at a synchronous speed proportional to the rotating field in the stator. In an IPM synchronous machine, typically, there is a stator with multiphase windings and a rotor that has interior permanent magnets mounted thereon.
In a conventional synchronous machine the rotor is intended to rotate within an embracing stator. The rotor poles extend radially outwardly and the stator poles radially inwardly. It is also known to arrange the machine such that an outer rotor has radially inwardly extending poles and the inner stator has radially outwardly extending poles.
The rotor may be transversely laminated and comprises a stack of laminations of a suitable ferromagnetic material. The laminations, each, define the profile of the rotor bore and a series of angularly arranged rotor poles. The axial bore receives a shaft for rotational motion. The laminations in this form of reluctance machine lie in planes which are perpendicular to the axis of rotation of the rotor.
Independent of the machine type, a cogging torque may be generated by the discontinuity of the stator lamination at the airgap. The discontinuity is caused by the teeth of the stator. During operation, cogging torque may reduce the efficiency of the motor and cause vibrations that can adversely affect both the motor and driven loads. Cogging torque also can degrade the quality of the product associated with the driven load. Lower cogging torque leads to decrease in transient losses in the reluctance machines as well as smoother reaction to electrical torque inputs.
There are a number of approaches to reduce or avoid cogging torque. Such approaches include rotor skewing which sectioning the core and introducing a relative angular rotation to each section. Another approach involves varying the shape of the magnets or the magnetization paths.
While various approaches have been taken to reduce or avoid such cogging, the aforementioned approaches have not provided a suitable solution. Accordingly, there is a need for a new approach to the problem of attenuating cogging torque.
The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of the prior art system.
The present disclosure describes a rotor for a synchronous machine, the rotor comprising a central axis; a bore being centrally positioned and extending axially relative to the central axis; a plurality of poles arranged around the bore, the poles extend axially in a direction parallel to the central axis; an air gap surface configured to face an air gap; and a plurality of slots mutually angularly spaced relative to the central axis wherein each slot extends axially in a direction parallel to the central axis and wherein each slot is adjacent the air gap surface.
The foregoing and other features and advantages of the present disclosure will be more fully understood from the following description of various embodiments, when read together with the accompanying drawings, in which:
This disclosure generally relates to a rotor for a synchronous machine having a low torque ripple effect.
The rotor 10 has an air gap surface X. The air gap surface X is the portion of the rotor 10 that borders an air gap in a synchronous machine. The air gap surface X faces onto the air gap. The air gap surface X is configured to face the air gap in a synchronous machine. The air gap surface X may be the internal surface 16 or the external surface 18 of the rotor 10. With reference to
With respect to
With reference to
Each slot 22 extends axially in a direction parallel to the central axis A. The slots 22 are configured as through passages. Each slot 22 is positioned adjacent the air gap surface X. The plurality of slots 22 is circumferentially adjacent to the air gap surface X. The plurality of slots 22 border on the air gap surface X. The slots 22 are positioned along the periphery of the rotor 12. Slots 22 are not contiguous with the air gap surface. The plurality of slots 22 is arranged so as to be concentrically aligned relative to the air gap surface X.
Generally, the number of slots 22 (including the flux barriers) may be selected using the following relationship: (1.25÷1.35)*Q, where Q is the stator slot number.
The slots 22 encircle the plurality of poles 14. The plurality of slots 22 form a discontinuous magnetic field barrier around the plurality of poles 22. In an embodiment, the slots 22 are positioned between the air gap surface X and the plurality of poles 14.
The slots 22 are calibrated in shape and size according to the size of the synchronous machine, stator slot number and rotor geometry. The shape of the slots 22 is selected from the group consisting of: circular, elliptical, disco-rectangular and triangular.
With respect to
The slots 22 encircle the plurality of the radially outwardly extending poles 14. The plurality of slots 22 form a discontinuous magnetic field barrier around the plurality of the radially outwardly extending poles 14. In an embodiment, the slots 22 are positioned between the external surface 18 and the plurality of the radially outwardly extending poles 14.
With respect to
The slots 22 encircle the plurality of the radially inwardly extending poles 14. The plurality of slots 22 form a discontinuous magnetic field barrier around the plurality of the radially inwardly extending poles 14. In an embodiment, the slots are positioned between the internal surface 16 and the plurality of the radially inwardly extending poles 14.
In an embodiment, the rotor 10 is transversely laminated. The rotor 10 comprises a plurality of transverse laminates 24 stacked along an axial direction of the rotor 10. The rotor 10 is formed through the aligned stacking in succession of a plurality of the transverse laminates 24. The transverse laminates 24 are shaped like discs and are constrained to one another to constitute a cylindrical structure that constitutes the rotor N.
Each laminate 24 is made of ferromagnetic material. Each laminate 24 comprises flux barriers 26. The flux barriers 26 are formed as voids in the rotor 10. The flux barriers 26 may be curvilinear, linear or chevron shaped. The flux barriers 26 are arranged in groups 26′ where each group constitutes a pole 14. In the illustrated embodiment, in each group 26′ a plurality of flux barriers 26 are formed in each quarter circumferential angular region in the rotor 10. The flux barriers 26 is a plurality of voids.
Flux guides 28 are positioned adjacent the flux barriers 26. Flux guides 28 are interposed between the flux barriers 26. Flux guides 28 are positioned between flux barriers 26 in each group 26′.
The flux barriers 26 are arranged to define the poles 14. The poles 14 are mutually angularly spaced about the central axis A. The groups of flux barriers 26′ are arranged equidistant from one another in the angular direction along the rotor 10. The plurality of slots 22 are positioned around the plurality of poles 14. The plurality of slots 22 are positioned around the groups of flux barriers 26′. The slots 22 are positioned around the flux barriers 26 and the flux guides 28 that define the plurality of poles 14.
The groups flux barriers 26′ are positioned adjacent the air gap surface X with the plurality of slots 22 positioned between the groups flux barriers 26′ and the air gap surface X. The plurality of slots 22 are positioned between the flux barriers 26′ and the air gap surface X. The plurality of slots 22 are positioned between the air gap surface X and the flux barriers 26 and the flux guides 28.
The dimension slots 22 may be varied in respect to the type and the dimension of the synchronous machine. In an embodiment, the dimension of the slot 22 may be approximately one half of the flux barrier height 26. In a rotor 10 with a plurality of flux barriers 26, the flux barrier 26 closer to the air gap surface X is used reference.
If the slot 22 is circular the dimension is the diameter slot 22. If the slot 22 is not circular, the dimension is the width of the slot 22 that is approximately equal to the height of the flux barrier 26. In a rotor 10 with a plurality of flux barriers 26, the flux barrier 26 closer to the air gap surface X is used reference. In any case the minimum height or width cannot be smaller than the thickness of each laminate 24.
In an embodiment, the rotor 10 may of the internally mounted permanent magnet type where torque is produced by the presence of the magnets. The magnets further provide rotor magnetization. In an internally mounted permanent magnet type rotor 10 the flux barriers 26 may be the magnetic pockets where the permanent magnets are inserted.
A single magnet 25 may define a pole 14. In an embodiment, a plurality of magnets 25 are grouped to define respective plurality of poles 14.
The positioning of the magnetic pockets 27 demarks the arrangement of the magnets 25. The slots 22 are positioned around the plurality of magnetic pockets 27. The plurality of magnetic pockets 27 are positioned adjacent the air gap surface X with the plurality of slots 22 positioned between the magnetic pockets 27 and the air gap surface X. The slots 22 are positioned around the plurality of magnets 25. The plurality of magnets 25 are positioned adjacent the air gap surface X with the plurality of slots 22 positioned between the magnets 25 and the air gap surface X.
In an embodiment, the rotor 10 may be of the permanent magnet assisted type.
In an alternative embodiment, with reference to
With reference to
With reference to
The synchronous machine may be configured as permanent magnet assisted reluctance machine (not shown) comprising a permanent magnet assisted type rotor 10. The synchronous machine may be configured as an internally mounted permanent magnet machine (not shown) comprising an internally mounted permanent magnet type rotor N.
The skilled person would appreciate that foregoing embodiments may be modified or combined to obtain the rotor 10 of the present disclosure.
This disclosure describes a rotor 10 for a reluctance machine. The rotor 10 is provided with a plurality of slots that enable the reduction or balancing of the magnetic flux fluctuation during rotation so as to reduce the cogging torque. The presence of the slots negates the alignment effect (reluctance effect) of the stator teeth and the rotor lamination. The slots are obtained directly on the rotor during lamination punching and stacking process.
Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein.
One skilled in the art will realize the disclosure may be embodied in other specific forms without departing from the disclosure or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the disclosure described herein. Scope of the disclosure is thus indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.
Number | Date | Country | Kind |
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19209788.9 | Nov 2019 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2020/082407 | 11/17/2020 | WO |