Abstract:
A system for generating power includes a homopolar electrical generator having, a superconducting field coil operative to create a magnetic field, and a homopolar rotor assembly operative to rotate in the magnetic field such that a rotating magnetic field couples with a stationary winding by an interaction of a rotating permeance wave produced by the homopolar rotor assembly and the magnetic field created by the superconducting field coil., and a wind turbine mechanically linked to the homopolar electrical generator operative to rotate the homopolar rotor assembly.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    An embodiment of the invention relates generally to superconducting homopolar alternators, and more particularly to systems involving using superconducting homopolar alternators for wind power applications. 
         [0002]    In this regard, superconducting homopolar alternators that include a superconducting field coil that is not installed on a rotor assembly are advantagious in multiple applications. Since superconducting field coils use cryogenic fluid to cool the coils, a non-rotating superconducting field coil simplifies the components used to deliver cryogenic fluid to the coils. Additionally, the electrical connections to the rotor assembly are simplified; since there are no coils on the rotor, electrical connections via brushes or other means are not present. Systems that utilize superconducting homopolar alternators that include a superconducting field coil that is not installed on a rotor assembly for power generation are desired. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    An exemplary embodiment includes a system for generating power comprising, a homopolar electrical generator having, a superconducting field coil operative to create a magnetic field, and a homopolar rotor assembly operative to rotate in the magnetic field such that a rotating magnetic field couples with a stationary winding by an interaction of a rotating permeance wave produced by the homopolar rotor assembly and the magnetic field created by the superconducting field coil, and a wind turbine mechanically linked to the homopolar electrical generator operative to rotate the homopolar rotor assembly. 
         [0004]    An alternate exemplary embodiment includes homopolar electrical generator system comprising, a superconducting field coil operative to create a magnetic field, and a homopolar rotor assembly including, a hub portion having an inner cavity partially defined by the hub portion, and a polar portion engaging an outer circumference of the hub portion having a plurality of poles, wherein the homopolar rotor assembly is operative to rotate in the magnetic field such that a rotating magnetic field couples with a stationary winding by an interaction of a rotating permeance wave produced by the homopolar rotor assembly and the magnetic field created by the superconducting field coil. 
         [0005]    Another alternate exemplary embodiment includes a homopolar electrical generator system comprising, a superconducting field coil operative to create a magnetic field, a homopolar rotor assembly including, a hub portion having an inner cavity partially defined by the hub portion, and a polar portion engaging an outer circumference of the hub portion having a plurality of poles, wherein the homopolar rotor assembly is operative to rotate in the magnetic field such that a rotating magnetic field couples with a stationary winding by an interaction of a rotating permeance wave produced by the homopolar rotor assembly and the magnetic field created by the superconducting field coil, and a wind turbine mechanically linked to the homopolar electrical generator system operative to rotate the homopolar rotor assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other features, aspects, and advantages will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0007]      FIG. 1  is an illustration of an exemplary embodiment of a system using a superconducting homopolar alternator. 
           [0008]      FIG. 2  is an illustration of a perspective partially cut-away view of an exemplary embodiment of a superconducting homopolar alternator system. 
           [0009]      FIG. 3  is an illustration of a perspective view of an alternate exemplary embodiment of a rotor assembly of the superconducting homopolar alternator system of  FIG. 2 . 
           [0010]      FIG. 4  is an illustration of a front view of an alternate exemplary embodiment of a rotor assembly of the superconducting homopolar alternator system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments. However, the embodiments may be practiced without these specific details. In other instances, well known methods, procedures, and components have not been described in detail. 
         [0012]    Further, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, or that they are even order dependent. Moreover, repeated usage of the phrase “in an embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising,” “including,” “having,” and the like, as used in the present application, are intended to be synonymous unless otherwise indicated. 
         [0013]    Superconducting homopolar alternators are used to generate electrical power. A wind turbine system having a superconducting homopolar alternator that has a superconducting field coil that is not installed on a rotor offers efficient and clean electrical power generation with a relatively small installed weight. 
         [0014]    Referring to  FIG. 1 , a wind turbine drive train system for generating electrical power  100  is shown. The system  100  includes wind blades  101 , a gear box  103 , and a superconducting homopolar alternator  105  mechanically linked to the wind blades  101  via the gear box  103  and shafts (not shown). A cable  107  is in electrical communication with the superconducting homopolar alternator  105  and a power grid (not shown) and often a power electronics conversion system (not shown). 
         [0015]      FIG. 2  illustrates a perspective partially cut-away view of an exemplary embodiment of a superconducting homopolar alternator system  200  that may, for example, be used in the system  100 . The superconducting homopolar alternator system  200  includes a homopolar rotor assembly  201  that includes poles  202 , linked to a shaft assembly  207 . The poles  202  comprise a ferro-magnetic material. The shaft assembly  207  engages bearings  209 . The illustrated embodiment further includes a stator yoke  203 , an armature  205 , and a superconducting field coil  211 . A cryocooler  215  and a re-condenser  213  are also included in the system  200 . For optimal power density, it is advantageous that the rotor assembly  201  and the yoke  203  compose of soft magnetic material with as high magnetic saturation and magnetic susceptibility as possible, and as low magnetic hysteresis as possible. The superconducting field coil  211  may be composed of any superconducting wire, such as NbTi, Nb 3 Sn, BSCCO, YBCO, or MgB 2 . The temperature supplied by the cryocooler  2   15  is determined by the operating characteristics of the superconducting wire employed. 
         [0016]    In operation, the superconducting homopolar alternator system  200  produces electrical power. The cryocooler  215  is operative to maintain a temperature in the superconducting field coil  211  that allows the superconducting field coil  211  to induce a magnetic field that surrounds the homopolar rotor assembly  201 . The cryocooler  215  may be any type of cryocooler that will maintain the proper temperature of the superconducting field coil  211 . The cryocooler  215  may operate with cryogenic liquids such as, for example, nitrogen and neon. The shaft assembly  207  is mechanically linked to the wind turbine  101  via the gear box  103  (of  FIG. 1 ). As wind turns the wind turbine  101 , the shaft assembly  207  rotates, and in turn, rotates the rotor assembly  201 . 
         [0017]    The rotating poles  202  in the homopolar rotor assembly  201  induce a permeance wave of magnetic flux. The flux produced by the rotating poles  202  causes a rotating magnetic field that passes through stationary windings in the stator yoke  203  (an armature winding). The rotating magnetic field generates a current flow in the stationary windings in the stator yoke  203 . In the illustrated embodiment the homopolar rotor assembly  201  rotates at approximately 200 revolutions per minute (rpm). The operational speed of the homopolar rotor assembly  201  will vary based on the speed of the rotation of the wind turbine  101  (caused by varying wind velocities) and the gear ratio of the gear box  103 . 
         [0018]      FIG. 3  illustrates a perspective view of an alternate exempliary embodiment of the homopolar rotor assembly  201 .  FIG. 3  includes a radial flux homopolar inductor alternator, however axial flux machines may also be used. A lightweight homopolar rotor assembly  300  is shown. The lightweight homopolar rotor assembly  300  includes a hub portion  301  having an outer surface  311  and optional inner cavities  303  partially defined by the hub portion  301 . A polar portion  305  engages an outer circumference  309  of the hub portion  301 . The polar portion  305  includes a plurality of poles  307 .  FIG. 4  illustrates a front view of the lightweight homopolar rotor assembly  300 .  FIG. 4  shows the outer surface  311  having openings  303 . The inner cavity and the openings  303  may be used to reduce the weight of the rotor. 
         [0019]    The use of the lightweight homopolar rotor assembly  300  allows the superconducting homopolar alternator system  200  to operate more efficiently in wind turbine applications. For optimal power density, it is advantageous that the rotor assembly  300  and its portions  301 ,  305 ,  307  to compose of soft magnetic material with as high magnetic saturation and magnetic susceptibility as possible, and as low magnetic hysteresis as possible. 
         [0020]    This written description uses examples to disclose the invention, including the best mode, and also to enable practice of the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope in an embodiment of the invention is defined by the claims, and may include other examples. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.