Abstract:
An apparatus for wind energy conversion includes a nacelle having a main frame, the main frame having a lower part and an upper part joined to the lower part, the upper part having a first strap extending across the lower part; a stator disposed within the nacelle; a rotor disposed within the nacelle; a mounting surface attached to the main frame and defining a rotor space, the mounting surface having a first side-face that exposes the rotor space; and a flange rotatably supported on the main frame and including a first end connected to the rotor. The rotor is cantilevered from the flange into the rotor space from the first side face.

Description:
FIELD OF DISCLOSURE 
       [0001]    The present disclosure relates generally to wind energy converters, and in particular, to a generator, a nacelle, and to mounting a nacelle of a wind energy converter. 
       BACKGROUND 
       [0002]    A wind energy converter is a rotating machine that converts the kinetic energy in wind into electricity and feeds the electricity into the electrical grid. 
         [0003]    A wind energy converter generally includes a nacelle disposed on a tower. The nacelle (also called a “gondola”) includes a rotor head equipped with blades, and a main shaft connected to the rotor head, also called hub, that integrally rotates with the rotor head. Moreover, the nacelle can rotate around a vertical axis so as to actively or passively follow the wind direction. 
         [0004]    A first type of nacelle further includes a gear box connected to the main shaft, which rotates upon receiving the wind power supplied to the blades, and a generator driven by an output shaft from the gear box. According to the wind energy converter having this structure, the rotor head equipped with the blades converts wind power into a torque, and the main shaft rotates to generate a first rotational speed. The first rotational speed is increased via the gear box connected to the main shaft, and a corresponding second larger rotational speed is transmitted to the rotor of the generator. 
         [0005]    A second type of nacelle, which lacks a gear box, uses direct drive turbines with AC generators having a variable frequency. Special high power electronics convert this variable frequency to constant frequency for transmission on the grid. 
         [0006]    In present wind energy converters, the nacelle must ultimately be on top of a tower. This often requires lifting the nacelle, or its constituent parts, using a crane. Such a task is quite difficult and complex because the components are massive. 
       SUMMARY 
       [0007]    In one aspect, the invention features an apparatus for wind energy conversion. The apparatus includes a nacelle having a main frame having a lower part and an upper part joined to the lower part. The upper part has a first strap that extends across the lower part. A stator and a rotor are both disposed within the nacelle. A mounting surface is attached to the main frame and defines a rotor space. The mounting surface has a first side-face that exposes the rotor space. A flange is rotatably supported on the main frame and includes a first end connected to the rotor. The rotor is cantilevered from the flange into the rotor space from the first side face. 
         [0008]    In some embodiments, the stator, the rotor, or both can include a superconductor. 
         [0009]    Other embodiments include those in which the first strap is configured to apply a radially inward force to the mounting surface, those in which the first strap is fastened to the mounting surface, and those in which the first strap conforms to an outer surface of the mounting surface. 
         [0010]    Embodiments of the nacelle also include those in which the mounting surface includes an integrated mounting plate configured to receive a fastener for fastening the first strap to the mounting surface. In some of these embodiments, the mounting plate includes a T-beam ring integral with the mounting surface. 
         [0011]    In additional embodiments, the nacelle includes a friction interface between the mounting surface and parts of the main frame. For example there can be a friction interface between the mounting surface and the first strap. In some of these embodiments, the friction compound is disposed between the integrated mounting plate and the first strap. Or there may be a friction interface between the mounting surface and the lower part of the main frame. 
         [0012]    Specific friction compounds can be found in some embodiments. For example, different embodiments of the nacelle include those in which the friction compound includes zinc. 
         [0013]    Additional embodiments include those in which the frictional force between the friction interface and the mounting surface are increased, for example by providing a series of bolts for coupling the housing to the first strap, to the lower part of the main frame, or both. 
         [0014]    Additional embodiments include those in which the upper part of the main frame has two or more straps extending across the lower part of the main frame. In such embodiments, a friction interface can be provided between the mounting surface and any combination of straps, and/or the lower part of the main frame. Bolts can also be provided to exert a force that increases the frictional force between the friction interface and any part of the main frame. 
         [0015]    In some embodiments, an outer surface of the stator defines the mounting surface. But in other embodiments, there is a generator housing within which the stator and rotor are disposed. In such cases, the mounting surface is defined by the outer surface of the generator housing. 
         [0016]    In another aspect, the invention features a method for assembling a wind energy converter. Such a method includes mounting a first part of a nacelle main frame on a tower, and mounting a rotatably supported flange, which includes a first end, on the first part of the main frame. A mounting surface that at least partially encloses the rotor space is then provided. The mounting surface has a first and second side face, in which first side face of the mounting surface exposes the rotor space. Spacers are provided in the rotor space. A rotor is inserted into the rotor space such that the spacers are positioned between the rotor and the stator. The mounting surface, including the inserted rotor, is mounted on the first part of the main frame. The first end of the flange is connected to the rotor. The spacers are then removed such that the rotor is cantilevered into the rotor space from the first side face. A first strap is connected to the first part of the main frame, the first strap extending across the first part of the main frame and conforming to the mounting surface. 
         [0017]    Additional practices of the invention include securing the first strap to the mounting surface. Securing the first strap can include fastening the first strap to a mounting plate integrated into the mounting surface, providing a friction interface between the mounting surface and the first strap, and/or fastening the first strap to a T-beam ring integrated into the mounting surface. 
         [0018]    In another aspect, the invention features a generator having a mounting surface at least partially enclosing a rotor space a mounting plate extending along at least a portion of the mounting surface; and a cantilevered rotor extending into the rotor space. The has a first and second side face. The first side face of the mounting surface exposes the rotor space. 
         [0019]    Embodiments of the generator include those in which the mounting plate includes a ring extending around the mounting surface. 
         [0020]    Additional embodiments include those in which the mounting surface is an outer surface of a generator housing, and those in which the mounting surface is an outer surface of a stator. 
         [0021]    Yet other embodiments include those in which a friction interface is disposed on the mounting surface. 
         [0022]    In a general aspect, a nacelle of a wind energy converter includes a main frame, a generator including a stator and a rotor, and a generator housing attached to the main frame and at least partially enclosing the stator and a rotor space. The generator housing has a first side face that exposes the rotor space. A flange is rotatably supported on the main frame and includes a first end connected to the rotor. The rotor extends into the rotor space from the first side face without being supported in the generator housing. 
         [0023]    In another aspect, a nacelle of a wind energy converter includes a main frame, a generator including a stator and a rotor, a generator housing attached to the main frame and at least partially enclosing the stator and a rotor space, and a flange rotatably supported on the main frame and including a first end connected to the rotor. The rotor extends into the rotor space without being supported in the generator housing. 
         [0024]    Embodiments may include one or more of the following. The flange includes a second end connected to a hub for attaching rotor blades. The generator housing is of substantially cylindrical shape, e.g., of cylindrical cup shape. The generator housing includes a first side face, the first side face exposing the rotor space. The generator housing includes a second side face opposite to the first side face, the second side face including at least one opening. 
         [0025]    The main frame is form-closed with an outer surface of the generator housing. The main frame includes a first part and a second part that are releasably connected with each other and that embrace, or conform to, the generator housing. An air gap between the stator and the rotor is at least 1 cm, e.g., between 1 cm and 5 cm. At least one of the stator and the rotor includes a superconductor. 
         [0026]    In a further aspect, a mounting method of a nacelle of a wind energy converter includes the steps of mounting a first part of a main frame on a tower, mounting a rotatably supported flange that includes a first end on the first part of the main frame, providing a generator housing at least partially enclosing a stator and a rotor space, providing spacers in the rotor space, inserting a rotor into the rotor space such that the spacers are positioned between the rotor and the stator, mounting the generator housing including the inserted rotor on the first part of the main frame, connecting the first end of the flange to the rotor, and removing the spacers such that the rotor extends into the rotor space without being supported in the generator housing. 
         [0027]    Embodiments may include one or more of the following. A second part of the main frame is mounted such that the first and second parts embrace the generator housing. The flange includes a second end. The method further includes the step of connecting the second end to a hub for attaching rotor blades. The step of mounting the flange includes mounting a bearing supported by a bearing housing on the first part of the main frame. 
         [0028]    In another aspect, a generator includes a stator, a rotor, and a generator housing at least partially enclosing the stator and a rotor space. The rotor extends into the rotor space without being supported in the generator housing. 
         [0029]    Embodiments may include one or more of the following. The generator housing is of substantially cylindrical shape, e.g., of cylindrical cup shape. The generator housing includes a first side face, the first side face exposing the rotor space. The generator housing includes a second side face opposite to the first side face, the second side face including at least one opening. 
         [0030]    An air gap between the stator and the rotor is at least 1 cm, e.g., between 1 cm and 5 cm. At least one of the stator and the rotor includes a superconductor. A cooling system is provided in the generator housing. A sensor is provided in the generator housing. 
         [0031]    With the generator described herein, it is possible to integrate a generator housing in a main frame that contains several components, e.g. generator and stator of the generator, but that does not support the rotor. By integrating this special generator housing in the main frame, the transport and mounting problems of the generator can be drastically reduced. 
         [0032]    The generator housing can furthermore include rigidity improvement parts. Depending on the housing rigidity, the mainframe rigidity can be supported or compensated. Generally, the rigidity of the housing is determined by the mainframe. Moreover, improved testability components can be included. The generator housing facilitates the whole generator testing process as there is only a need for a single separate mounted bearing and rotor. 
         [0033]    The cylindrical housing can be fully or partially closed/open on the rear side. With this construction, a device can be mounted that allows easy integration of the housing into the mainframe and also easy extraction of the housing from the mainframe. 
         [0034]    It is preferred that the housing be a cylindrical housing. If the cylindrical form is chosen for the housing, only torsion forces are transferred into the cylindrical housing. 
         [0035]    With an open rear side construction, the generator can be very easily assembled from or disassembled into constituent parts. This feature eases the task of maintaining the integrated components in the housing. 
         [0036]    Integrated temperature measuring systems linked to a cooling and heating circuit can be provided to monitor the temperature and, depending on the monitored temperature, to start or stop the integrated cooling or heating circuits. 
         [0037]    A generator and a nacelle as described herein provide significant advantages. The generator housing offers protection to integrated sensitive components during transport and mounting. Fixing the generator housing into an already mounted tower and a partially mounted or completely mounted nacelle is much easier than lifting and mounting a completely pre-assembled nacelle. 
         [0038]    All these above-mentioned advantages will help to reduce the overall cost in wind turbine manufacturing by easing the tasks of transport and assembling, by providing integrated cooling and/or heating, and by improving rigidity. The simplified testing conditions also contribute significantly to cost reduction. 
         [0039]    Further aspects are illustrated in the accompanying drawings and described in detail in the following part of the description. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0040]      FIGS. 1   a,b  are cross-sectional views showing an example of the internal structure of one embodiment of a nacelle, with  FIG. 1   a  being a longitudinal cross-section along the blade rotational axis A, and  FIG. 1   b  being a transverse cross-section of the generator along the nacelle rotational axis B indicated as A-A′ in  FIG. 1   a;    
           [0041]      FIGS. 2   a - c  a show a mounting surface from  FIG. 1   a , with  FIG. 2   a  being a vertical cross-section along the blade rotational axis A,  FIG. 2   b  being a plain side view of the side S 1 , and  FIG. 2   c  being a plain side view of the side S 2 ; 
           [0042]      FIGS. 3   a - c  show another example of a mounting surface that may be used in the nacelle of  FIG. 1   a , in which  FIG. 3   a  is a plain side view of the side S 1 ,  FIG. 3   b  is a vertical cross-section along the blade rotational axis A, and  FIG. 3   c  is a plain side view of the side S 2 ; 
           [0043]      FIGS. 4   a,b  are cross-sectional views for illustrating a mounting method of the nacelle of  FIGS. 1   a  and  1   b;    
           [0044]      FIG. 5  is a side view showing an example of the overall structure of a wind energy converter; 
           [0045]      FIG. 6  is an isometric view of an alternative nacelle; 
           [0046]      FIG. 7  is a transverse view of the alternative nacelle of  FIG. 6 ; and 
           [0047]      FIG. 8  is a close-up of a portion of the alternative nacelle of  FIG. 6 . 
       
    
    
       [0048]    Throughout the figures the same reference numbers indicate the same or functionally equivalent parts. It should be noted that the individual figures for explaining specific modes of operation do not include all details, but just the details needed for explaining the respective mode. 
       DETAILED DESCRIPTION 
       [0049]      FIG. 5  is a side view showing an example of the overall structure of a wind energy converter. A wind energy converter  1  includes a tower  2  disposed on a foundation  6 , a nacelle  3  provided on the upper end of the tower  2 , the nacelle being rotatable around a substantially vertical axis B, and a rotor head  4  provided on the nacelle  3  including a hub (not shown) for fixing rotor blades  5 , with the rotor head  4  being rotatable around a substantially horizontal axis A. 
         [0050]    Blades  5  extending radially from the rotation axis A are attached to the rotor head  4  at different circumferential angles. Wind power supplied to the blades  5  from the direction of the variable rotation axis A of the rotor head  4  rotates the rotor head  4  around the rotation axis. 
         [0051]      FIGS. 1   a  and  1   b  are cross-sectional views showing an example of the internal structure of a nacelle, with  FIG. 1   a  being a longitudinal cross-section along the blade rotational axis A, and  FIG. 1   b  being a transverse cross-section along the nacelle rotational axis B indicated as A-A′ in  FIG. 1   a.    
         [0052]    The nacelle  3  includes a mainframe  10  having a lower part  10   a  and an upper part  10   b  that together enclose a cylindrical space (see  FIG. 1   b ) defined by the cylindrical inner surface O 1  of the lower and upper parts  10   a ,  10   b.    
         [0053]    The upper part  10   b  is fixed to the lower part  10   a  by bolts  13 ,  14  mounted in flanges  11   a ,  12   a  integrally provided in the lower part  10   a  and flanges  11   b ,  12   b  integrally provided in the upper part  10   b.    
         [0054]    The lower part  10   a  and the upper part  10   b  surround, or conform to a mounting surface  20 , which can be either the outer surface of a cylindrical generator housing or the surface of a stator  30   a . In those embodiments in which the mounting surface  20  is the outer surface of a generator housing, the stator  30   a  and a rotor space  21  for accommodating a rotor  30   b  are within the generator housing. The generator housing is a pre-assembled part that can be separately mounted between the lower and upper parts  10   a ,  10   b  of the mainframe  10 , separately from the rotor  30   b.    
         [0055]    In either case, at least one of the stator  30   a  and rotor  30   b  includes a superconductor. 
         [0056]    The mounting surface  20  has a first side face S 1  and a second side face S 2 . In this example, the second side face S 2  is fully closed such that the mounting surface  20  forms a cylindrical cup. 
         [0057]    The first side face S 1  is open and exposes the rotor space  21 . A cylindrical bearing  45  supported by a bearing housing  46  is mounted between the lower and upper parts  10   a ,  10   b  of the mainframe  10  to rotatably support a flange  40  having a first and second end E 1 , E 2  and which exhibits a Y-shaped cross-section along axis A. 
         [0058]    The first end E 1  of the flange  40  is connected to the rotor  30   b , which is inserted into the rotor space  21  through the first side face S 1  of the mounting surface  20  in a way that avoids contacting any neighboring structures. In other words, the rotor  30   b  extends into the rotor space  21  from the first side face S 1  without further support. The rotor  30   b  is therefore a cantilevered rotor that is only supported by the flange  40 , which is inserted into the bearing  45 . Thus, in contrast to known structures, the structure disclosed herein uses only a single bearing  45 . This reduces the construction complexity and the costs. 
         [0059]    An air gap  25  between the rotor  30   b  and the stator  30   a  in this example amounts to about 2.5 cm because the stator coils in this example are superconducting coils that are cooled via pipes (not shown). Another air gap  26  exists between the distal end of the rotor  30   b  extending from the flange  40  and the second side face S 2  of the mounting surface  20 . This additional gap  26  typically amounts to several centimeters. 
         [0060]    Depending on the mechanical tolerances of the bearing  45  and the other generator components, the air gap  25  may be made smaller than 2.5 cm. However, for air gaps  25  below 1 cm it is difficult to realize such an arrangement with a single bearing  45 . As a result, for such air gaps, it is preferable to provide a further bearing outside the mounting surface  20 . An additional bearing may also become useful because of deformations resulting from loads acting on the rotor head  4 , such as wind loads and weight loads. 
         [0061]    Furthermore, attached to the second end E 2  of the flange  40  is a hub  50  for attaching rotor blades (not shown). The rotor, together with the flange  40  and the attached hub  50 , is rotatable around a horizontal axis A while driven by the wind acting on the rotor blades. 
         [0062]    A further flange  60  is attached to the lower part  10   a  of the mainframe  10 . The flange  60  is supported by a bearing  70  provided on the top of the tower  2 . The bearing  70  enables the nacelle  3  to rotate about a vertical axis B, which in turn enables it to actively follow wind direction. The nacelle  3  actively follows wind direction using gear drives  80  that act on the inner periphery of the flange  60  in a conventional manner. The lower part  10   a  of the mainframe  10  and flange  60  can be integrated together to form a single part. 
         [0063]      FIGS. 2   a - c  are different views showing an embodiment in which the mounting surface  20  is the surface of a cylindrical generator housing of  FIG. 1   a .  FIG. 2   a  is a vertical cross-section along the blade rotational axis A,  FIG. 2   b  is a plain side view of the side S 1 , and  FIG. 2   c  is a plain side view of the side S 2 . 
         [0064]    As is apparent from  FIGS. 2   a - c , the mounting surface  20  is closed on its second side face S 2  and open on its first side face S 1  so that the rotor  30   b  can be easily inserted into the rotor space  21  from the open side face S 1  after the mounting surface  20  has been mounted on the lower part  10   a  of the mainframe  10 . 
         [0065]      FIGS. 3   a - c  are different views showing another example of a mounting surface that may be used in the nacelle  FIG. 1   a .  FIG. 3   a  is a plain side view of the side S 1 ,  FIG. 3   b  is a vertical cross-section along the blade rotational axis A, and  FIG. 3   c  is a plain side view of the side S 2 . 
         [0066]    In the example shown in  FIGS. 3   a - c , further components are integrated into the mounting surface  20 ′. Among the components are cooling and/or heating elements  100   a ,  100   b  and integrated sensors  101   a ,  101   b  for sensing the temperature in the vicinity of the stator  30   a  and/or rotor  30   b . Both the sensors  101   a ,  101   b  and heating/cooling elements  100   a ,  100   b  have corresponding connection openings in the second side face S 2 . 
         [0067]    A maintenance opening  24  in the side face S 2  of the cylindrical mounting surface  20 ′ provides access to the generator components. With an open rear side construction, the generator can easily be assembled from or disassembled into parts. This construction eases the task of maintaining integrated components in the housing. 
         [0068]      FIGS. 4   a,b  are cross-sectional views for illustrating a mounting method of the nacelle of  FIG. 1   a,b.    
         [0069]    With regard to  FIG. 4   a , in a first step the first bearing  70  is mounted on top of the tower  2 . 
         [0070]    Then, flange  60  is connected to the lower part  10   a  of the mainframe  10 . Thereafter, the bearing  45  supported by the bearing housing  46  and the flange  40  are mounted on the lower part  10   a  of the mainframe  10 . The preassembled parts  10   a ,  60 ,  45 ,  46 , and  40  are lifted together and mounted on top of the tower  2 . 
         [0071]    In a following step, the gear drives  80  for rotary motion of the nacelle  3  around the vertical axis B are installed in known manner. This leads to the configuration shown in  FIG. 4   a.    
         [0072]    In a next step, as illustrated in  FIG. 4   b , the rotor  30   b  is inserted into the rotor space  21  such that the rotor  30   b  extends into the rotor space  21  from the first side face S 1  without contacting the stator  30   a . During assembly, air gap spacers  47  separate the rotor  30   b  and stator  30   a , and a gap  26  separates the mounting surface  20  from the rotor  30   b . The air gap spacers  47  in the air gap  25  (e.g. bumpers) thus serve to protect the stator  30   a  during the mounting process. 
         [0073]    Then, the mounting surface  20 , including the inserted rotor  30   b , is lifted onto the lower part  10   a  of the mainframe  10 . In this example, the mounting surface  20  conforms to the cylindrical surface O 1  of the lower part  10   a  of the mainframe, such that self-alignment can be achieved. 
         [0074]    Thereafter, the flange  40  is connected to the rotor  30   b  at its first end E 1  using a fastener, such as a nut or a bolt. 
         [0075]    Finally, the air gap spacers  47  are removed and the upper part  10   b  of the mainframe  10  is mounted on top of the lower part  10   a  so as to surround the bearing  45  and the mounting surface  20  and to establish a fully form-closed arrangement. The fixing of the lower and upper parts  10   a ,  10   b  of the mainframe  10  is then achieved by fixing bolts  13 ,  14 , shown in  FIG. 1   b . The hub  50  is then connected to the end E 2  of the flange  40  by fasteners, such as nuts or bolts. This results in the structure shown in  FIG. 1   a.    
         [0076]    Further steps such as attaching the rotor blades and cable and piping connections will not be explained here since they are well known in the art. 
         [0077]    In another embodiment, the upper part  10   b  of the mainframe  10  includes front and rear straps  82 ,  84  that extend along an arc in a direction perpendicular to the horizontal axis A of the nacelle  3 , as shown in isometric view in  FIG. 6  and in transverse cross-section in  FIG. 7 . Both the front and rear straps  82 ,  84  are screwed into, or otherwise attached to the lower part  10   a  of the mainframe  10 . 
         [0078]    The front and rear straps  82 ,  84  wrap around the mounting surface  20 , as shown in  FIG. 6 . In so doing, they apply a compressive, or radially inward force to the mounting surface  20 , thus holding it securely in position. 
         [0079]    The mounting surface  20  includes front and rear mounting plates extending along at least a portion thereof. In one embodiment, the mounting plates are integrated T-beam rings  86 ,  88 , best seen in  FIG. 7 . To more securely engage the straps  82 ,  84 , it is useful to pass bolts  92 ,  94  or screws through the straps  82 ,  84  to engage the T-rings  86 ,  88 , as shown in  FIG. 8 . In addition, it is useful to provide a friction interface  90  between the straps  82 ,  84  and their corresponding T-rings  86 ,  88 , as shown in  FIG. 8 . 
         [0080]    A friction interface  90  can be provided by applying a friction compound between the straps  82 ,  84  and their corresponding T-rings  86 ,  88 . A suitable friction compound for this purpose is a silicate primer. One example of such a primer is a zinc-rich ethyl silicate primer. One example of a zinc-rich primer includes 85% zinc by dry weight. A suitable primer is sold under the name “INTERZINC 22” by International Protective Coatings. 
         [0081]    A friction interface  90  can also be provided between the lower part  10   a  and the mounting surface  20 . The force exerted by the frictional interface  90  can be enhanced further by providing bolts are other fasteners for squeezing together the surface  20  and the lower part  10   a  and/or the surface  20  and the straps  82 ,  84 . For example, in the case in which a T-rings  86 ,  88  extend all the way around the surface  20 , the friction interface  90  can be provided all along the T-rings  86 ,  88 . In such cases, one can also provide bolts or similar fasteners periodically or aperiodically all along the T-rings  86 ,  88 . 
         [0082]    As a result of replacing the solid upper part  10   b  of the mainframe  10  with two compressive straps  82 ,  84 , the overall weight of the upper  10   b  is significantly reduced, thus easing the task of raising the upper part  10   b  and assembling the nacelle  3 . 
         [0083]    Although the present invention has been described with reference to embodiments, it is not limited thereto, but can be modified in various manners which are obvious for a person skilled in the art. Thus, it is intended that the present invention is only limited by the scope of the claims attached herewith. 
         [0084]    In particular, the present invention is not limited to the cylindrical geometry shown in the embodiments, but applicable for any geometry.