Abstract:
Wind turbine direct drive alternator system includes a supporting structure, at least two turbines mounted on the supporting structure to rotate in opposite directions when exposed to the same wind, a respective number of alternator rotor disks whereby each turbine is directly connected to an alternator rotor disk, and a stator unit having two sides each facing a respective rotor disk. The stator unit is arranged or constructed such that torque generated by rotation of each turbine can be transmitted therethrough with a view toward balancing the torque induced on the supporting structure by rotation of the turbines. When the stator unit includes two stator disks, each stator disk transmits approximately the same magnitude of torque as, but in an opposite direction to, the other stator disk. The two stator disks balance the torque of each other and almost no external torque is needed to balance the system.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a wind energy generating system that can be airborne, fixed to a ground-based tower or situated offshore, and more specifically to a wind energy generating system that includes multiple turbines and a direct drive alternator system that are arranged to minimize and possibly eliminate induced torque on the system. 
     BACKGROUND OF THE INVENTION 
     In order to produce electricity from a wind turbine, the rotations of the wind turbine are typically transferred to an alternator, directly or through an intervening transmission system. Output power of the alternator is a result of the multiplication of the rotational speed of the wind turbine (in radians per second) by the torque (in Newton-meters) that is acting on a rotor of the alternator. 
     There is a trend to increase the span of wind turbines in order to capture more wind power; however, the rotational speed of the wind turbines has decreased. As a result, the torque induced by the wind turbine on the alternator rotor has increased accordingly. For example, for a 1 mega watt wind turbine rotating at 30 rpm (3.14 radians/second), the torque induced on the alternator rotor while producing 1 MW will be” 
     Torque=1,000,000 W/3.14 radians/second=318471 Newton-meter=32.5 metric tons. This enormous torque must be balanced by the construction of the wind turbine wherever it is placed, i.e., on the ground, offshore or in the air. 
     OBJECTS OF THE PRESENT INVENTION 
     it is an object of at least one embodiment of the present invention to provide a wind energy generating system including a plurality of wind turbines and an alternator system that are torque balanced, i.e., the torque that the turbines and alternator induced on other sections of the system will be almost zero. 
     Another object of at least one embodiment of the present invention is to provide a wind energy generating system with a direct drive alternator, i.e., the does not have a transmissions. 
     Yet another object of at least one embodiment of the present invention is to provide a wind energy generating system that can be used with different types of wind turbines, whether mounted to the ground, mounted offshore over a body of water or airborne. 
     Still another object of at least one embodiment of the present invention is to provide a wind energy generating system that will be light-weight and have a relatively low cost to produce. 
     Accordingly, one embodiment of a wind energy generating system in accordance with the present invention comprises a supporting structure, at least two turbines rotatably mounted on the supporting structure and arranged to rotate in opposite directions when exposed to the same wind, a respective number of alternator rotor disks whereby each turbine is directly connected to one of the alternator rotor disks, and a stator unit including at least two stator disks that are mechanically connected to or integral with each other such that each stator disk transmits approximately the same magnitude of torque as, but in an opposite direction to, the other stator disk. As such, the two stator disks balance the torque of each other and almost no external torque is needed to balance the wind energy generating system, with respect to induced torque on the supporting structure. 
     Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like elements, and wherein: 
         FIG. 1  is a side view, partially in cross section, shows turbines and an alternator section of a wind energy generating system in accordance with the invention; 
         FIG. 2  is a view along line p-p of  FIG. 1  through the turbines blades and shows the profile and angle of the blades; 
         FIG. 3  is a detailed drawing of segment  100  of the wind energy generating system shown in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line A-A of  FIG. 3 ; 
         FIG. 5  is an arrangement of one segment of the permanent magnet of the wind energy generating system in accordance with the invention; 
         FIG. 6  is a front view of one of the rotor disks of the wind energy generating system in accordance with the invention; 
         FIG. 7  is a front view of one of the stator disks of the wind energy generating system in accordance with the invention; 
         FIG. 8  is a side view of the wind energy generating system operating as an airborne version; 
         FIG. 9  is a front view of the wind energy generating system, operating as a ground-based version; 
         FIG. 10  is a cross-sectional view of the wind energy generating system shown in  FIG. 9  with a connecting element that connects the wind energy generating system to a ground-based or offshore tower; 
         FIG. 11  is a side view of the connecting element of  FIG. 10 ; 
         FIG. 12  is a side view, partially in cross-section, of a second embodiment of a wind energy generating system in accordance with the invention which is based on magnetic flux in a radial direction; 
         FIG. 13  is a partial view of the turbine section of the wind energy generating system showing another embodiment of a stator unit in accordance with the invention; 
         FIG. 14  is a partial view of the turbine section of the wind energy generating system showing yet another embodiment of a stator unit in accordance with the invention; 
         FIG. 15  is a schematic of one electricity processing system that delivers DC current from the wind energy generating system in accordance with the invention; and 
         FIG. 16  is a side view, partially in cross-section, of another embodiment of the wind energy generating system in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the accompanying drawings wherein the same reference numerals designate the same or similar elements, a wind energy generating system in accordance with the invention is designated generally as  10  and comprises two turbines, each including two turbine blades  107  and  117 , and which turbines are arranged to have opposite rotational directions when exposed to the same wind. Additional turbines and turbine blades may be provided. 
     Wind turbine blades  107  and  117  are connected to hubs  109  by connecting elements  108 , and wind turbine blades  107  are connected through a hub  109  to a front bearing housing  110  while wind turbine blades  117  are connected through a hub  109  to a rear bearing housing  114 . The bearing housings  110  and  114  allow the turbines with turbine blades  107  and  117 , respectively, to rotate freely around a rotation axis defined by a main shaft  115  and transfer their rotational motion to rotor disks  104 . Bearings  111  are placed inside the bearing housings  110  and  114  to enable rotation of the bearing housings  110  and  114  relative to the main shaft  115 . Bearings  111  may be conical type bearings, or other type of bearings that can support axial and radial forces. The main shaft  115  has a hole  113  therein through which electrical wires (not shown) may pass, for example as shown by wires  175  and  176  in  FIG. 16 . 
     Wind energy generating system  10  also includes alternators components. The segment designated  100 , enlarged in  FIG. 4 , shows a segment of a permanent, rotor magnet  103 , a rotor disk  104 , a stator magnetic core  101 , a pre-winding coil  102  and a stator disk  105 . The stator magnetic core  101 , in this embodiment of the system, has a generally C-shape and it can be produced by any of the following technologies: laminations, c-cores, unicore and other technologies that are known in the industry. The pre-winding coil  102  can be assembled on the magnetic core  101 , and this method will make the stator winding process more economical, but other methods of coil winding can be used. The combination of the stator magnetic core  101  and the pre-winding coil  102  constitute a conductive coil assembly. Each rotor disk  104  is arranged relative to the facing one of the stator disks  105  such that the magnets  103  on the rotor disks  104  generate a magnetic field that encompasses the conductive coil assemblies on the stator disk  105 . 
     Rotor magnet  103  is one of the system&#39;s permanent magnets which will be shown in detail in  FIG. 5 . The wind generating system  10  includes at least two rotor disks  104 , shown in detail in  FIG. 6 , each rotor disk  104  is arranged to be rotated upon rotation of a respective wind turbine with turbine blades  107  or  117 . Wind generating system  10  also includes at least two stator disks  105 , shown in detail in  FIG. 7 , each of which is at least partly opposed to a disk-shaped portion of a respective rotor disk  104 . 
     Connecting elements  106  are arranged between the at least two stator disks  105  and transfer the opposite directional torques between the stator disks  105  and enable the torque-balancing in accordance with the invention. The number of connecting elements  106  can vary and in the illustrated embodiment of the invention, there are eight connecting elements  106 . The shape of the connecting elements  106  can vary and in the illustrated embodiment, they have a substantially cylindrical shape. Thus, different numbers and shapes of connecting elements are envisioned in the invention. 
     A supporting cylinder  112  connects the stator disks  105  to the main shaft  115 . Supporting cylinder  112  allows a center positioning of the stator disks  105  and the rotor disks  104  relative to each other, as well as connection of the wind generating system  10  to a ground-based or offshore tower, shown in detail in  FIGS. 9-11 . 
     Magnetic cores and/or coils  119  are placed around the stator disks  105 , represented by dotted lines. Also, permanent magnetic elements  120  are placed around the rotor disks  104 , also represented by dotted lines. 
       FIG. 2  shows a cross-sectional profile and angular position of the turbine blades  107  and  117  along line p-p in  FIG. 1 . The profile of the turbine blades  107  and  117  is preferably identical. However, the angle of attack of the turbine blades  107  and  117  relative to a direction of the wind  135  is different from one another and arranged to produce opposite rotational movement in that the turbine with turbine blades  107  rotates in the direction of arrow  116  while turbine with turbine blades  117  rotates in the direction of arrow  118  while exposed to wind in the same direction  135 . 
       FIG. 3  shows segment  100  of  FIG. 1  including one magnetic core  101 , two pre-winding coils  102 , two permanent magnets  103 , a plate  121 , part of the stator disk  105 , and part of the rotor disk  104 . Plate  121  may comprise iron. The magnetic core  101  is preferably made from laminations of silicon steel, that provide the magnetic core  101  with a generally U-shape with the pre-winding coils  102  being placed around the two arms of the U-shaped magnetic core (see  FIG. 4 ). The number of windings and the cross-sectional area of the winding wire can be adjusted according to the electrical requirements of the alternator. The U-shaped magnetic core  101  and the pre-winding of coils thereabout allow a more accurate and more economical production process of the coils. Other winding techniques and magnetic core shapes can be used in the invention. 
       FIG. 4  shows segment  100  in a cross-sectional view along line A-A in  FIG. 3 . Permanent rotor magnets  103  are attached to the plate  121 , e.g., affixed or glued thereto, to provide the configuration shown in  FIG. 5 . The permanent rotor magnets  103  are preferably NDFeB type magnets that are very strong permanent magnets, although other types of magnets can be used. The assembly of two permanent rotor magnets  103  on the plate  121  is designed to create a maximum magnetic flex through the magnetic core  101 , when the two permanent rotor magnets  103  are positioned next to the arms of the U-shaped magnetic core  101 . 
       FIG. 6  shows the rotor disk  104  with a plurality of magnetic assemblies connected to an annular portion thereof, with each assembly comprising a plate  121  and two permanent rotor magnets  103  affixed thereto. The material of the rotor disk  104  is preferably aluminum, fiber glass and/or carbon fiber, although other materials can be used. The plate  121  may be omitted in some embodiments so that the permanent rotor magnets  103  are attached directly to the rotor disk  104 , e.g., glued thereto. Reference  122  designates the locations of the other magnetic assemblies that are not shown in  FIG. 6 . In the illustrated embodiment, an angle  125  between the centers of adjacent ones of the magnetic assemblies is about ten degrees. A center hole  123  of a central portion of the rotor disk  104  fits the outside diameter of a mating portion of a respective one of the bearing housings  110  and  114  (see  FIG. 1 ). Holes  124  extending through the rotor disk  104  enable the rotor disk  104  to be connected to the bearing housings  110  and  114 . Spoke portions connect the central portion with the center hole  123  to the annular portion to which the magnet assemblies are mounted. The wind energy generating system  10  in accordance with the present invention has at least two rotor disks  104 , and the source of the magnetic flux of the rotor disks  104  is preferably permanent magnets but other type of magnets such as electromagnets can be used. 
       FIG. 7  shows a front view of the stator disk  105 , which in this embodiment has a plurality of pairs of rectangular holes  126  in an annular portion. Magnetic cores  101  are attached to the stator disk  105  such that the arms of each magnetic core align with and possibly extend through a respective pair of holes  126  (see  FIG. 4 ). Other methods for attaching the magnetic cores  101  to the stator disk  105  can be used in the invention and as noted above, other shapes and forms of magnetic cores can be used. The stator disk  105  itself can be formed as part of the magnetic cores. In one embodiment, coils without magnetic materials are attached to the stator disk  105 . 
     A center hole  130  of a central portion of each stator disk  105  fits the outside diameter of supporting cylinder  112 . Holes  131  extending through each stator disk  105  enable each stator disk  105  to be connected to the supporting cylinder  112 . Holes  132  are used to connect the connecting elements  106  to the stator disks  105  so that via the connecting elements  106 , the two stator disks  105  are connected to one another to allow torque to be transmitted from one stator disk  105  to the other. 
     Instead of constructing the stator disks  105  as separate units, each mounted about the supporting cylinder  112 , it is possible to construct the two stator disks  105  as one stator unit. For example,  FIG. 13  shows the stator unit  106 A as an integral unit with two disk-shaped portions on lateral sides wherein one disk-shaped portion  106 B has a face oriented toward one rotor disk  104  and the other disk-shaped portion  106 C has a face oriented toward the other rotor disk  104  and integral connecting struts  106 D extend therebetween. Another envisioned construction of the stator unit is as a single disk-shaped member  106 E as shown in  FIG. 14 , one side of which faces one rotor disk  104  and the other side of which faces the other rotor disk  104  so that connecting elements  106  are not necessary. However, in one or both of these embodiments, each section of the stator unit, which may be considered as a stator disk, should have sets of coils that are exposed to magnetic flex from a rotating rotor while at least two rotor disks are rotating in opposite directions. Thus, the stator unit defines two disk-shaped portions each facing a respective rotor disk  104 , whether on the same integral member or separate members that are connected together. 
     The angles between the centers of the magnetic cores are designated  127 ,  128 , and  129 . In the illustrated embodiment, there are twelve sets of magnetic cores, so that when the angles  127 ,  128 ,  129  are equal, they all equal thirty degrees. If the angles are not equal, e.g., angle  127  is 33 degrees, angle  128  is 36 degrees and angle  129  is 21 degrees, low, no-load idle resistance of the system is obtained because all magnets and magnetic cores will not be at same maximum attraction angular position together. This angular differential arrangement will cause a differential in the phases of the output of the coils. The output electricity of the system can be multi-phase AC or each conductive coil assembly can be converted to DC and all of the DC outputs can be connected in a serial connection. 
     To this end, with reference to  FIG. 15 , a plurality of conductive coil assemblies  160  is shown and each is connected to a respective rectifier  162 . Each rectifier  162  has a positive and negative output with the negative output of one rectifier  162  being connected to the positive output of another rectifier  162 , in serial, with a single positive and negative output being provided from all of the rectifiers  162 . This construction will result in a high DC voltage output. 
     The number of magnetic assemblies and the number of the magnetic cores can vary from those shown in the drawings so that any number of magnets and magnetic cores can be used in the invention. 
     Referring now to  FIG. 12 , in the embodiments described above, the magnetic structure is arranged to generate magnetic flux is an axial direction. In the embodiment shown in  FIG. 12 , the magnetic structure is arranged to generate magnetic flux in the radial direction. Differences between this embodiment and the embodiments described above lie primary in the magnetic structure and otherwise, the same components of the wind energy generating system  10  may be used in this embodiment. This embodiment includes at least two rotor disks  204  rotatably mounted about a central shall represented by line  215 , permanent rotor magnets  203  arranged on the rotor disks  204 , two stator disks  205  fixedly mounted to the central shaft, connecting elements  206  that connect the stator disks  205  together, a plurality of magnetic cores  201  arranged on the stator disks  205 , and pre-winding coils  202  arranged in connection with the magnetic cores  201 . The connecting elements  206  function like connecting elements  106  to connect the stator disks  205  together to allow torque to be transmitted between the stator disks  205 . The operations and torque-balancing in this embodiment are the same as explained above, with the main difference being that the direction of the magnetic flux is radial because the magnetic cores  201  are radially outward of the rotor magnets  203 . 
       FIG. 8  shows the wind energy generating system  10  of the present invention operating as an airborne wind turbine. To this end, a lifting section  144  is coupled to the wind energy, and lifting section  144  may be a blimp containing a lighter-than-air gas such as helium. The lifting forces that act on the blimp are a floating force that the lighter-than-air helium creates, and the lift that is created by the aerodynamic shape of the blimp when acted upon by wind. The lifting forces of the blimp are transmitted through tethers  142  and  143  to the wind energy generating system  10  allowing the wind energy generating system to be airborne and operate at high altitude. Construction element  140  is interposed between and connects the main shaft  115  to the tether  143  and is arranged to cause the center of gravity of the airborne system to be lower than a virtual line connecting a point at which the tether  141  is connected to the wind energy generating system  10  and a point at which the tether  143  is connected to the wind energy generating system  10 . As such, this position creates a pendulum effect that keeps the wind energy generating system  10  balanced with respect to torque. Tether  141  is connected to a winch  145  on the ground. 
       FIG. 9  shows the wind energy generating system  10  operating on the ground (or offshore) at an upper end of a vertical member  150  that may be any type of pole or tower that anchors the main shaft  115  to the ground or to the sea floor. This anchoring may be achieved using a base  151  and connecting screws  152 , 
       FIGS. 10 and 11  show exemplifying structure that may be used to support the main shaft in a fixed position relative to the ground or sea floor. The connecting structure includes a connecting element  155  that interacts with the supporting cylinder  112  that is fixedly mounted to the main shaft  115 . The connecting element  155  has a lower portion defining a groove in which the supporting cylinder  112  rests and an upper portion that covers the supporting cylinder  112  and each of the lower and upper portions has flanges with holes  156  through which connecting members, such as screws, are placed to connect the lower and upper portions together with the supporting cylinder  112  and thus the main shaft  115  fixedly supported therebetween. 
     Referring now to  FIG. 16 , in this embodiment of the invention, the rotor assembly has only a single rotor disk  104  and the remaining structure to provide for rotation of the rotor disk  105  upon rotation of the turbine including turbine blades  107  is the same as in the embodiment shown in  FIG. 1 . However, instead of another rotor disk  104  or other rotor member and a stator unit including a pair of stator disks  105 , the embodiment shown in  FIG. 16  includes a second rotating assembly that serves the same function as the stator disk  105  in the embodiment shown in  FIG. 1 . This second rotating assembly includes a single member such as a disk  105 A that rotates relative to the rotor disk  104  and in an opposite direction thereto, e.g., while the front turbine including turbine blades  107  causes rotation of the rotor disk  104  in one direction when exposed to wind via the bearing housing  110 , the rear turbine including turbine blades  117  causes rotation of the disk  105 A in an opposite direction via the bearing housing  114  when exposed to the same wind. As in the embodiments described above, the rotor disk  104  includes magnets and associated structure and encompassing variations, and the rotating disk  105 A includes conductive coil assemblies that were provided on the stator disk  105  in the embodiments above. The rotor disk  104  and rotating disk  105 A are spaced apart such that the conductive coil assemblies and magnets are within a magnetic field of one another. 
     The electricity that is generated in the conductive coil assemblies on the disk  105 A can be directed to pass through rectifiers described in connection with  FIG. 15  and conducted to two conductive rings  173  and  174  arranged on the bearing housing  114 . The DC electricity is then conducted through two conductive brushes  171  and  172  that are arranged in a non-conductive cylinder  177  fixed to the main shaft  115 . The electricity passes through wires  175  and  176  connected to the brushes  171  and  172  for use and/or storage. 
     The combination of the single rotor disk  104  with magnets and single rotating disk  105 A with conductive coil assemblies may be repeated on the same shaft  115 . 
     Advantages of this embodiment of the invention include: by arranging the conductive coil assemblies on a rotating disk  105 A (as opposed to on the non-rotational stator disk  105 ) and causing this rotating disk  105 A to rotate in an opposite direction to the rotor disk  104  and such that the conductive coil assemblies are within a magnetic field range of the magnets on the rotor disk  104 , the relative velocity between the magnets on the rotor disk  104  and the conductive coil assemblies on the rotating disk  105 A is doubled. Since the power of the alternator is proportional to this relative velocity, a higher power from the same alternator can be achieved or a lower cost alternator can be built while achieving the same power (in comparison to a case wherein the alternator is associated with a construction wherein a stator disk with the conductive coil assemblies is non-rotational relative to the rotor disk). Another advantage is that lighter alternators can be built according to this embodiment, which is important for airborne wind turbines, as well as for ground-based and off shore wind turbines. Yet another advantage is that the opposite directional torques are being transferred from the rotor to the rotating disk and from the rotating disk to the rotor electrically, without need of special construction elements. 
     It is to be understood that the present invention is not limited to the embodiments described above, but includes any and all embodiments within the scope of the following claims. While the invention has been described above with respect to specific apparatus and specific implementations, it should be clear that various modifications and alterations can be made, and various features of one embodiment can be included in other embodiments, within the scope of the present invention.