Patent Application
20150171673
This disclosure relates generally to synchronous reluctance machines and specifically to rotor structures of synchronous reluctance machine.
A synchronous reluctance machine has a stator and a rotor supported in the inner periphery of the stator, is capable of being locally excited and is structurally the same as the stator of a common induction machine. Generally, the synchronous reluctance machine is well known as a motor, which is simply structured and does not need electric current carrying conductors or permanent magnets in the rotor. For example, the conventional induction machine comprises a machine body serving as a casing, a stator arranged along an inner circumferential surface of the machine body and an AC squirrel cage rotor rotatably arranged based on a rotational shaft at the center of the stator. The stator is formed of a lamination structure of various compositions of silicon steel and is provided with a plurality of teeth therein. A number of slots are formed between the teeth with a certain interval and the coil is wound on the teeth through the slots.
The synchronous reluctance rotor generally includes a plurality of rotor sections formed of alternating magnetic and non-magnetic components stacked axially and secured to a shaft. The core has a central axial bore for receiving a shaft. The laminations or laminated sections are inserted between radially extending arms of the core that are formed with a smooth, arcuate recess therebetween. The laminations are secured in the recesses by means of radial fasteners that secure radially opposing rotor sections to the core. The rotor sections are also secured together by end flanges and radial fasteners. The end flanges are cup-shaped members with an axially extending outer rim that is disposed about the outermost periphery of the laminations. The radial fasteners extend through the end flanges and core to secure the end flanges to the rotor. The rotor laminations may also be bonded to one another and to the core using an epoxy or other adhesive material.
Existing synchronous reluctance machines are mechanically and structurally limited because, traditionally, one set of designs uses axial laminations of various shapes and sizes assembled to make a rotor. In such examples, typically adhesives are used to retain the laminations. The non-uniformity of lamination parts poses an assembly problem for such designs. Further, it is an engineering requirement to resist the reactive centrifugal forces on the laminations and thereby reduce the leakage in magnetic flux.
Further, another set of traditional designs uses axially stacked laminations, having iron bridges to retain the laminations. These iron bridges have high leakage making these machines power deficient. Prior attempts in the past to remedy this problem have considered placing non-magnetic support notches between the arcuate lamination layers, while using non-magnetic discs at either ends of the machine to retain the support notches. Such an attempt typically uses similar shaped support notches that reduces complexity but raises several new manufacturing related issues.
Therefore there is need to improved mechanical structure with enhanced torque density and higher resistance to centrifugal force in the laminations.
The disclosed technology is a rotor assembly that includes at least one integral non-magnetic rotor retaining structure comprising a plurality of individual rotor retaining discs, the discs having predefined slots; and a plurality of magnetic segments retained within the slots of the discs of the respective integral non-magnetic rotor retaining structure.
In another embodiment, the disclosed technology is a synchronous reluctance machine that includes a stator; a rotor shaft operationally disposed within the stator; a plurality of non-magnetic segments; a plurality of magnetic segments forming a rotor about the rotor shaft; and a plurality of non-magnetic segments integrated into a rotor retaining structure configured to retain the plurality of magnetic segments.
In yet another embodiment, the disclosed technology is a synchronous reluctance machine that includes a stator; a rotor shaft operationally disposed within the confines of the stator; a plurality of selected laminated magnetic segments arranged to form a rotor about the rotor shaft; and an integral rotor retaining structure with a plurality of non-magnetic segments having varying sizes, shapes and thicknesses.
In a further embodiment, the disclosed technology is a method for assembling synchronous reluctance machine that includes forming a rotor, assembling the rotor onto a rotor shaft; and providing a stator and operationally disposing the rotor and the rotor shaft therein. The step of forming a rotor includes providing a non-magnetic rotor retaining structure; and retaining a plurality of selected laminated magnetic segments disposed on the non-magnetic rotor retaining structure.
The above described and other features are exemplified by the following figures and detailed description.
Referring now to the figures wherein the like elements are numbered alike:
The disclosed technology relates to a rotor structure used in a synchronous reluctance machine. According to one embodiment, the rotor is formed from a plurality of magnetic segments that are retained into the desired shape by a retaining structure that allows the magnetic segments to be inserted for easy assembly.
Referring to
In one embodiment, the non-magnetic segments are designed as a number of intermediate discs to support the laminated magnetic segments 28, 32, and so on, in the axial direction.
In another embodiment, the non-magnetic segments are designed as a number of notches formed on the intermediate discs to support the laminated magnetic segments in the radial and circumferential directions.
Whether in the form of notches or grooves, the non-magnetic segments 22, 24, and so on, may, if desired, be any convenient shape or size to separate the laminated segments. Depending on the design criteria of the synchronous reluctance machine the non-magnetic segments 22, 24, may be of varying size within the rotor pole structure. For example, the non-magnetic segments 22, 24, of exemplary pole 17 are all the same size, have an elongated shape and traverse the axial length of each associated arcuate structure. The non-magnetic segments 22, 24, and the rotor retaining structure 26, in one example are manufactured from a non-ferromagnetic material that provides high strength, particularly at higher temperatures. Examples of such non-ferromagnetic materials include materials such as Inconel, AM 350 or 17-4PH.
Referring again to
The introduction of non-magnetic material as a retaining structure allows for minimizing or completely removing the iron bridges or bolts typically used in traditional design of rotors for electric machines, thereby improving the torque density of these machines. Further, by placing the non-magnetic material between the laminations in the rotor, the non-magnetic material improves the mechanical structure by resisting the centrifugal force in the laminations. Overall, the non-magnetic material helps overcome the problem of assembly and improves the torque density in machines.
As delineated above the synchronous reluctance machine 10 has axially stacked magnetic segments 28, 32, and so on, which significantly reduce the core losses. Each of the lamination segments is “locally” supported by non-magnetic notches (or grooves) 22, 24, and so on, intermediate discs 42, 44, and so on, and end flanges 46 so that its mechanical load is not wholly transferred to the next one. This makes the rotor more robust and allows for higher speed and larger diameter designs. Also, intermediate discs 42, 44, and so on support the lamination segments magnetic segments 28, 32, and so on axially, radial and circumferentially. These notches (or grooves) with the spacing among the lamination segments and the local support structure provide for assembly of the whole rotor from its constituent parts and help in structurally retaining the rotor in a very efficient manner.
In operation: the rotor shaft 16 along with poles 17, 18, 19 and 20 containing the laminated segments 28, 32, and so on, are rotatively disposed to the rotor which is supported by the inner peripheral surface of the stator 12 casing. Electrical AC power is supplied to the windings of the stator 12 and the rotor begins to rotate.
In one alternate embodiment, the disclosed technology may take the form commonly referred to as the “inside-out” configuration. In such a configuration, the axial laminations may form arcuate segments radially and the assembly of segments may be located radially outside of the stator 12. The stator 12 may then contain a plurality of windings and slots and may be located inside of the rotor 14. In yet another embodiment, the disclosed technology may be applied in such a way that the “inside-out” configuration is used to provide a double-sided machine. The axially stacked laminations, in one such design, can be used to form radially spaced segments that occupy space between an inner and an outer stator assembly (not shown). Conversely, a set of laminated segments may be assembled for rotating a structure radially inside the stator structure while other lamination segments are positioned radially outside the stator 12.
While the disclosed technology has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosed technology. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosed technology without departing from the essential scope thereof. Therefore, it is intended that the disclosed technology not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosed technology, but that the disclosed technology will include all embodiments falling with the scope of the appended claims.
