Patent Publication Number: US-2009224550-A1

Title: Systems involving superconducting direct drive generators for wind power applications

Description:
BACKGROUND 
     Embodiments of the invention relate generally to superconducting generators, and more particularly to systems involving superconducting direct drive generators for wind power applications. 
     In this regard, superconducting generators have been made by constructing the generator field coils (which typically carry a substantially direct current) of a superconducting material (“superconductor”) instead of the usual copper material. Superconductors are typically lighter in weight and smaller in size (e.g., relative to current carrying capacity) than traditional conductors such as copper and are also more efficient at conducting current (particularly at lower frequencies). Thus, the use of superconductors in wind power applications, such as wind turbine generators, provides benefits such as more efficient performance, lower generator weight, non-gearbox direct drive operation, and lower manufacturing and installation costs. However, superconductors require a very cold operating temperature (e.g., approximately −269 to −196 degrees Celsius or 4 to 77 Kelvin) to be superconducting and, while superconductors have zero resistance when carrying a non-alternating (“DC”) current, the resistance increases as the frequency increases when carrying an alternating (“AC”) current, which causes losses in the form of heating that counter the foregoing benefits. As a result, the armature coils of superconducting generators (which typically carry a higher frequency AC current) have still been constructed of copper. However, the use of superconductors for armature coils of superconducting generators used in wind power applications is desirable. 
     BRIEF DESCRIPTION 
     Systems involving superconducting direct. drive generators for wind power applications include, in an exemplary embodiment, a superconducting direct drive wind generator that includes an armature coil constructed of a first superconducting material and a field coil constructed of a second superconducting material, wherein, during operation of the generator, the armature coil and the field coil are in electromagnetic communication and the field coil produces a magnetic field in response to an excitation current flow therethrough that induces an output current flow in the armature coil that generates an electrical power output. 
     Another exemplary embodiment includes a system for generating power including a superconducting generator that includes an armature coil constructed of a first superconducting material and a field coil constructed of a second superconducting material, wherein, during operation of the generator, the armature coil and the field coil are in electromagnetic communication and the field coil produces a magnetic field in response to an excitation current flow through it which induces an output current flow in the armature coil. that generates an electrical power output, and a turbine rotor connected to the generator in a direct drive configuration. 
     Another exemplary embodiment includes a wind turbine power system including a superconducting generator that includes an armature coil constructed of a superconducting material and attached to a rotor of the generator and a field coil constructed of the superconducting material and attached to a stator of the generator, and a turbine rotor connected in a direct drive configuration to the generator via a shaft connected to the rotor of the generator, wherein a rotation of the turbine rotor rotates the armature coil in a proximity to the field coil which generates an electrical power output from the armature coil when a current is input through the field coil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is an illustration of an exemplary wind power system including a superconducting generator in accordance with exemplary embodiments of the invention. 
         FIG. 2  is an illustration of an exemplary cross sectional view of the superconducting generator from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Further, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present 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. 
     Superconducting generators (e.g., generators with one or more superconducting components) provide lighter weight, smaller size, and more efficient operation than traditional generators of the same or similar capacity and, thus, are beneficial in wind power applications such as wind turbine systems. Direct drive superconducting generators can operate at a low enough frequency to allow the inclusion of superconducting armature coils in addition to superconducting field coils to provide an even higher degree of the foregoing benefits in wind power applications. 
       FIG. 1  illustrates an exemplary wind power system  100  that includes a superconducting generator  102  in accordance with exemplary embodiments of the invention. The exemplary system  100  also includes a turbine rotor  104  that includes one or more blades  105 . The turbine rotor  104  is connected to the generator  102  in a direct drive configuration. For example, the turbine rotor  104  may be connected to the generator  102  via a shaft  106 . The generator  102 , one or more portions of the turbine rotor  104 , the shaft  106 , and other components (not depicted) of the wind power system  100  may be at least partially contained within a housing  10 . 8  that may also be referred to in the art as a “nacelle.” 
     The generator  102  and the turbine rotor  104  are supported by a support structure  110 , which is a structure capable of supporting these components, e.g., above the ground or other surface. As depicted., the support structure  110  may. also support the housing  108 , including the components contained therein. Although not depicted, a power carrying conductor (e.g., a cable) can be connected to an output of the generator  102  and extend down the support structure  110  (e.g., internally or externally) to connect to a power grid (e.g., a generation, distribution, and/or transmission system). 
       FIG. 2  illustrates an exemplary cross sectional view of the superconducting generator  102  from  FIG. 1 . As depicted, the generator  102  includes an outer concentric component  204  and an inner concentric component  206 . In some embodiments, the outer component  204  may be a stator (i.e., stationary portion) of the generator  102 , and the inner component  206  may be a rotor (i.e., rotating portion) of the generator  102  (e.g., in an internal rotor configuration). However, in other embodiments, the outer component  204  may be a rotor of the generator  102 , and the inner component  206  may be a stator of the generator  102  (e.g., in an external rotor configuration). A gap (or “air gap”)  205  is included between the outer component  204  and inner component  206  and allows movement (e.g., rotation) therebetween. Furthermore, in some embodiments, the shaft  106  may be connected to the inner component  206  as depicted, while in other embodiments, the shaft  106  may be connected to the outer component  204 . 
     The generator  102  also includes a first set of one or more current carrying conductors (“coil(s)”)  208  attached to the outer component  204  and a second set of one or more current carrying conductors (“coil(s)”)  210  attached to the inner component  206 . During operation of the generator  102 , these coils  208 ,  210  are in electromagnetic communication. In some embodiments, coils  208  may be armature coils of the generator  102 , and coils  210  may be field coils of the generator  102 . In other embodiments, coils  208  may be field coils of the generator  102 , and coils  210  may be armature coils of the generator  102 . In such embodiments, the field coil is connected to a source of excitation current (e.g., an “exciter”), which current flow therethrough produces a magnetic field across the field coil, and the armature coil is connected to the output of the generator  102  (e.g., via output terminals) to conduct an output current and electrical power output. Although several coils  208 ,  210  are depicted, there may be more or less coils  208 ,  210  and/or windings thereof about the outer component  206  and inner component  208  respectively in various embodiments, e.g., to configure the number of poles of the generator  102  and, thereby, the generating frequency and/or other operating characteristics of the generator  102 . 
     The field coils, e.g., coils  210 , are constructed of a superconducting material, such as niobium-titanium (NbTi), niobium-tin (Nb 3 Sn), or magnesium-boron (MgB 2 ). Furthermore, in accordance with exemplary embodiments of the invention, the armature coils, e.g., coils  208 , are also constructed of a superconducting material, such as NbTi, Nb 3 Sn, or MgB 2 , instead of copper as in traditional superconducting generators. In some embodiments, the coils  208 ,  210  are constructed of different superconducting materials, while in other embodiments they are constructed of the same superconducting material. Furthermore, in some embodiments, the armature coils  208  and/or the field coils  210  may be constructed of a high temperature superconductor (HTS), such as bismuth strontium calcium. copper oxide (e.g., BSCCO-2212 or BSCCO-2223) or yttrium barium copper oxide, (e.g., YBa 2 Cu 3   07  or “YBCO”). 
     In an exemplary operation, wind passes over the blades  105  thereby causing the turbine rotor  104  to rotate. This rotation causes a corresponding rotation of the rotor of the generator  102  (e.g., the inner component  206 ), which may occur, e.g., via the shaft  106 , since the generator  102  is connected to the turbine rotor  104  in a direct drive configuration. As a result, the field coil (e.g., coil  210 ) rotates in proximity to the armature coil (e.g., coil  208 ). An excitation current that is, e.g., substantially DC (e.g., approximately one hertz or less) is caused to flow through the field coil  210 , e.g., via an exciter. The field coil  210  produces a magnetic field in response to this excitation current flow, and the magnetic field induces an output current flow in the armature coil  208  as the field coil  210  is rotated in proximity to the armature coil  208 . The output current flow coupled with the voltage produced across the armature coil  208  generates an electrical power output from the generator  102  to a grid, e.g., via a power cable. 
     As a direct driven generator  102 , the generator  102  is configured to operate at a speed of approximately ten to twenty-five revolutions per minute (rpm) and to induce an armature current with a frequency of approximately one to ten hertz (Hz) (or cycles per second). This low-frequency characteristic allows the use of a superconducting armature coil  208  without countering or negating the benefits of the superconducting materials, e.g., due to heating losses that would occur in traditional wind power system superconducting generators that operate (e.g., gearbox driven) at higher speeds and produce higher frequency armature coil currents. 
     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 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.