Abstract:
An embodiment of Vertical Axis Wind Turbine (VAWT) concept with vanes coupled to central shaft thorough supports that are connected in such a way that vanes can be moved closer or further away from the central shaft of the wind turbine. The rotational speed of the wind turbine can be regulated by adjusting the distance of the vanes. Additionally, the turbine can be put into storm protection mode by bringing the vanes right next to the central shaft where the profile of the wind turbine is reduced to minimum.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the national stage entry under 35 USC 371 for PCT/IB2010/055317, filed Nov. 22, 2010. The contents of the foregoing application are incorporated herein by reference. 
     FIELD 
     The present invention relates to a wind turbine generator, more specifically, a wind turbine generator with rotation axis substantially at right angle to the direction of wind that includes a support column and rotor with multiple blades attached to the support column. 
     BACKGROUND 
     Wind turbine is the most popular way of harvesting wind energy. Wind generators are categorized as Horizontal-axis Wind Turbine (HAWT) and Vertical-axis Wind Turbines (VAWT). Researchers Erikson, Bernhoff and Leijon compared VAWT and HAWT designs in their article tided “Evaluation of different turbine concepts for wind power” which is published in Renewable &amp; Sustainable Energy Review issue 12 published in 2008. According to this article, HAWT design which most commercial wind farms utilize are considered complicated due to yaw mechanism which orients the turbine toward the wind and pitch mechanism which regulates the speed of the propeller. The article also mentions that HAWT designs are hard to maintain due to the fact that generator assembly is placed high above the ground. These mechanisms complicate the HAWT design and makes maintenance difficult due to the fact that all these mechanisms are placed high above the ground. The article also mentions that HAWT designs have almost reached their maximum possible size for megawatt level applications due to cyclically reversing gravitational loads on their blades. 
     Vertical-axis Wind Turbines (VAWT) may seem simpler in terms of structure due to the fact that they do not require to be oriented toward the wind. According to Erikson et al., this omni-directional nature of the turbine makes it very attractive for locations where wind frequently changes its direction. However, VAWT design has also has its own complications. Theoretically the efficiency of VAWT design is less than the efficiency of HAWT design due to the active area of the turbine which faces the wind. The theoretical maximum power coefficient of wind turbines is called Betz limit and found to be Cp=0.59. For HAWT designs this factor of performance is between 0.40 and 0.50. In case of VAWT designs this factor is found to be no more than 0.40 [Erikson et al.] Another factor of VAWT design that negatively affects the efficiency is the fact that while one of the vanes of VAWT is exposed to wind and converting the wind energy, another vane is being moved against the wind to continue the rotation of the turbine. 
     Despite all these negative points, mechanical simplicity of VAWT makes it very attractive for commercial wind farm applications. According to the literature, VAWT turbines can be packed denser than HAWT turbines since that cause less turbulence. Despite all this VAWT designs are rarely used for commercial wind farm applications. Currently VAWT has two major obstacles which impede its commercial applicability. These are;
         1. Storm protection. When wind speed reaches gale force level, there should be a mechanism to shut down the turbine and mechanically protect the structure and the vanes of the turbine from damage. This is not available with traditional VAWT designs like Savonius, Darrius and H-rotor design.   2. Speed regulation. There is a need for a speed control mechanism to regulate the rotational speed of the turbine so that power generated is less dependent on the wind speed.       

     These two problems are the main obstacles toward the commercialization of VAWT design. Recently there are attempts to solve these two problems. One of the most notable attempts is a patent filed by Sullivan with publication number US 2010/0172759 which uses airfoil shaped vanes and a mechanism for retracting vanes toward the rotational shaft on demand. The mentioned design is very similar to H-rotor design with retraction and storm protection capability added. 
     Erikson et al. states in their mentioned research that VAWT design essentially operate in drag mode, which limits the speed of rotation and requires larger blade area than the HAWT designs. These trade-offs are acceptable as long the cost of manufacture of blades are reduced. 
     SUMMARY 
     The purpose of the invention is a modification of VAWT design which has storm protection capability as well as speed regulation capability. The invention uses articulated vanes for VAWT design which can be raised or lowered automatically to regulate the angular speed of rotation of the turbine. The articulated vane design also enables the vanes to be lowered fully in case of excessive wind speed which puts the turbine in storm protection mode. Even though the efficiency of VAWT design is theoretically lower than commercial HAWT&#39;s, these two features of the invention enable us to scale up the VAWT design which may make up for the lower efficiency. 
     The articulated vanes of the turbine can be raised toward the top part of the main pillar in order to hunt for wind when wind speed is lower than expected. 
     The main feature of the design is its scalability for megawatt level applications. The articulation mechanism used in the design is string and pulleys, which can carry the weight of the vanes even if the span of the vanes, are excessively large. Another feature of the design is the use of soft vanes, which can be manufactured using soft sails, which gives the ability to scale up the design from manufacturing perspective, also reduce the cost of manufacture of vanes. Even though such features limit the speed of rotation of the wind turbine by confining the turbine to “drag” mode of operation, the design makes up its lost efficiency by being able to scale up for large size with reasonable cost of manufacturing. The design differs from US 2010/0172759 application by the use of soft vanes and the retraction mechanism of string assembly on top and bottom part of the vanes, which can lift or lower the vanes without relying on gravity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows the overall appearance of the turbine with the vanes in fully extended form. 
         FIG. 2  shows the detail of the hinge mechanism of the vanes and the connection to the central post. 
         FIG. 3  shows mechanism of an embodiment to raise or lower the vanes attached to the central rotating shaft. 
         FIG. 4  shows vanes lowered in speed regulation mode. 
         FIG. 5  shows the mode where the vanes are raised high above the central rotational shaft to catch wind. 
         FIG. 6  shows the storm protection mode where the vanes are lowered fully to reduce the wind exposure of the turbine. 
         FIG. 7  shows an embodiment of the vane made from soft material in high drag and low drag coefficient form. 
         FIG. 8  shows an embodiment of the vane design where the shutters of a vane are closed to increase the drag coefficient of the vane. 
         FIG. 9  shows the details of the shutter mechanism of embodiment of a vane in closed shutter mode. 
         FIG. 10  shows an embodiment of vane design where the shutters of the vane are open to decrease the drag coefficient of the vane. 
         FIG. 11  shows the details of the shutter mechanism of a vane in open shutter mode. 
         FIG. 12  shows the block diagram of the turbine system. 
     
    
    
     DESCRIPTION 
     The detailed description of the operation of the wind turbine is explained in this section. The  FIG. 1  shows the overall appearance of the preferred embodiment of the turbine with vanes extended fully. The design is a typical vertical axis wind turbine (VAWT) design that the vanes  21 ,  34  are connected to a central rotating shaft  26  to transfer the rotary motion to generator housing  20 , which is located at the base of the turbine structure. As the wind  33  blows, the vanes  21  exposed to the wind are moved by the drag force acting on them and the turbine turns in clockwise direction. The clockwise rotation moves the vane  34  on the opposite side toward the wind  33 . The vanes are designed in such a way that, the drag coefficient of the vane  34  on the opposite side of the wind  33  are lower than drag coefficient of vanes on windward side vane  21  which causes the turbine to turn. 
       FIG. 2  shows the details of the connection mechanism of a preferred embodiment. The vane  21  is attached to the central rotating shaft  26  through struts  23  and  25 . The struts  23 ,  25  are hinged at  27  and  22  so that vane  21  can move freely up and down at these hinge points. The movement mechanism of the vanes is shown in  FIG. 3 . The up and down movement of the vane  21  is controlled by string  24  which is attached to central rotating shaft  28  through pulley  29  situated at the top of the pillar  28 . One end of the string  24  goes through central rotating shaft  28  and reaches control room  20  located at the base of the turbine structure. By pulling the string  24 , the position of the vane  21  can be adjusted.  FIG. 4  shows the turbine vanes in lowered state by way of extending the length of the control string  24 , and by shortening the length of control string  41  located at the bottom of vane  21 . The strings  41  and  24  work in conjunction in such a way that when one gets longer, the other one gets shorter. The string assembly  41  and  24  control the level of extraction of the vane  21  together. The vanes  21  of the turbine can also be raised toward the top level of the central rotating shaft  28  as shown in  FIG. 5 . In this figure, the control string  24  is shortened by being pulled through central rotating shaft  28  so that the vanes  21  are raised to the level of the tip of the central rotating shaft  28 . This feature may be handy when wind velocity is low. As it is known generally, wind velocity increases with increasing altitude. 
       FIG. 6  shows the storm protection mode of the turbine where the control string  24  is let out as much as possible, control string  41  is shortened as much as possible, so that the vane  21  is lowered to the lowest possible height and gets situated right next to the central rotating shaft  26 . In this particular position the turbine has very slim profile and can withstand high wind velocity. 
     FIGS.  7 , 8 , 9  and  10  shows embodiments of the vane design which can be used with this turbine.  FIG. 7  shows an embodiment of the soft vane contemplated to be used with this invention.  7 -A shows the vane  51  which is made of sail cloth like soft material. The soft material is supported by rigid elements horizontally positioned at the top part  53  and in the middle positioned vertically  54 . These rigid elements guide the sail  51  where to get folded and opened under the influence of the wind force  33 . The soft vane  51  is free to get folded or opened along the axis  54 .  7 -A shows the soft vane  51  in open form where the drag coefficient of the vane  51  is high.  FIG. 7-B  shows the soft vane  51  in closed form where the soft vane material gets folded along the axis  54  guided by rigid top element  53 . In this particular form, the drag coefficient of the vane  51  is low since it maintains a low profile against wind  33 . 
       FIGS. 8 and 9  shows another embodiment of the vane design which is rigid.  FIG. 8  shows the top view of the vane  21 , which is made up of plurality of shutters  31 .  FIG. 9  shows the details of the shutter  31  which is airfoil shaped and hinged at point  32 . Under the influence of the wind  33  blowing toward the vane  21 , the shutters  31  close and vane develops high drag coefficient, which in turn causes the vane  21  to turn in direction of  34 . 
       FIGS. 10 and 11  shows the embodiment of the design shown in  FIGS. 8 and 9  in low drag coefficient form.  FIG. 10  shows the vane  21  moving toward the wind  33 , where the plurality of shutters  31  open and reduce the drag coefficient of the vane  21 .  FIG. 11  shows the details of the shutter  31 , which is hinged at point  32 . As the vane  21  turn in the direction of  34 , the shutter  31  moves toward the wind  33 , the lift force generated by the airfoil  35  is counteracted by the centripetal force  36  acting on the hinged shutter, which keeps the shutter  31  in open position. 
     The net effect of high drag force on some vanes and low drag force on others keeps the turbine rotating. 
       FIG. 12  shows the operation of the turbine system. Computing hardware and software  61  accept inputs from wind sensors  63  and power demand information  64  in analog or digital form and make up decision about the level of retraction of the vanes of turbine  65 . The decision is given to actuator  62 , which controls the strings  24  and  41  mentioned in  FIGS. 3 and 4 . When the wind speed is excessive, the information received from  63  indicates storm condition, which is decided by  61  and instructs actuator  62  to retract the vanes of turbine  65  to storm protection mode.