Abstract:
Wind turbine system. The system includes a lower wind speed vertical axis wind turbine operatively connected to a first electrical motor/generator and a higher wind speed vertical axis wind turbine operatively connected to at least one second electrical motor/generator. Electrical power from the first electrical motor/generator is directed to the at least one second electrical motor/generator and mag-lev system to cause the higher wind speed turbine to begin turning.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a wind turbine system and more particularly to a composite vertical axis wind turbine system that utilizes a lower wind speed vertical axis wind turbine to start the rotation of a higher wind speed wind turbine. 
     Wind energy is rapidly emerging as one of the most cost-effective forms of renewable energy with an ever-increasing installed capacity around the world. One of the widely recognized types of turbines used for electricity generation is the well-recognized Horizontal Axis Wind Turbine (HAWT). This type of turbine features a high blade tip velocity ratio, relatively high power generation efficiency, and low start-up torque. The second major group of wind turbines is the Vertical Axis Wind Turbines (VAWT), which possess several inherent advantages over HAWTs: VAWTs do not have to be yaw-adjusted to follow the changing direction of prevailing wind, and consequently handle gusts more efficiently; the power generator can be integrated into the system at ground level, reducing the structural requirements of the support tower, are much quieter in operation, lower in vibration and bird-friendly. However, a major disadvantage of most VAWT configurations is that they require a relatively high start-up torque. An omnidirectional vertical wind turbine electric generator system has been disclosed in U.S. Pat. No. 7,109,599 to Watkins. The contents of this patent are incorporated herein by reference. 
     Because of typical blade configurations and mechanical stiction in vertical axis wind turbines, it is known that starting a vertical axis wind turbine requires a higher wind speed than is necessary to keep the turbine rotating once it is in motion. Relatively smaller vertical axis wind turbines will start at lower wind speeds such as, for example, 3 miles per hour, whereas larger-sized units would require a higher wind speed (say 8 miles per hour) to start but might continue to rotate, once having been started, at, for example, 5 miles per hour. 
     It is an object of the present invention to address this major deficiency of VAWT by proposing a double-vertical-axis-turbine system with a torque-amplifying cascade arrangement. This system features a small vertical axis turbine that starts at a relatively lower wind speed which, once up to speed, subsequently starts a relatively higher wind speed vertical axis wind turbine. 
     SUMMARY OF THE INVENTION 
     In one aspect, the wind turbine system according to the invention includes a lower wind speed vertical axis turbine operatively connected to a first electrical motor/generator. A higher wind speed vertical axis wind turbine is provided and is operatively connected to at least one second electrical motor/generator. Electrical power from the first electrical motor/generator is directed to at least one second electrical motor/generator to start the higher wind speed turbine. In a preferred embodiment, the lower wind speed vertical axis wind turbine is disposed on top of the higher wind speed vertical axis wind turbine. It is preferred that the higher wind speed vertical axis wind turbine be operatively connected to two second electrical motor/generators. 
     In another preferred embodiment, the system includes an anemometer to measure wind speed such that the output of the anemometer is operatively connected to the first electrical motor/generator to direct power to the at least one second electrical motor/generator when measured wind speed reaches a selected level. Power electronics are provided to distribute electrical power from the first and second electrical motor/generators. 
     In one embodiment, the lower wind speed turbine includes five blades and the higher wind speed turbine includes three blades. It is preferred that the lower wind speed turbine be designed to begin rotating at a wind speed of approximately 3 miles per hour. A suitable higher wind speed turbine is designed to “self-start” turning at a wind speed of 8 miles per hour but once started, can run at say 5 miles per hour. 
     The wind turbine system disclosed herein is designed for mounting on building rooftops although other locations are appropriate. It is preferred that the turbines be selected to provide power in the range of 10 kW to 30 kW. The lower wind speed turbine and the higher wind speed turbine may share a common shaft. The blades of the turbines may be conventional wings with a high performance cambered airfoil configuration, featuring high lift-to-drag ratios. The blades may include regions with different surface textures and treatments. 
     An auxiliary blade that deploys at an angle to the main blades by use of a passive tail to serve as a wind directing and accelerating scoop blade that can swerve at an angle of say 30° to 40° off the prevailing wind may be provided, as in a sailboat&#39;s jib changing the mainsails&#39; apparent wind and increasing the surface area of the overall “sail” area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a perspective, schematic view of an embodiment of the invention disclosed herein. 
         FIG. 2  is a perspective view of another embodiment of the invention. 
         FIG. 3  is a block diagram showing the power electronics arrangement. 
         FIG. 4  is a schematic illustration (plan view) of an auxiliary accelerator blade according to another embodiment of the invention. 
         FIGS. 5   a  and  5   b  are perspective views of turbine blades showing surface treatments including micro vortex generators and dimples to cause the wind to be “stickier” on portions of the blade closer to the center of the hub to equalize and maximize pressure on the blade surface. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown schematically in  FIG. 1 , the wind turbine system  10  includes a lower wind speed vertical axis wind turbine  12  mounted above a higher wind speed vertical axis wind turbine  14 . An anemometer  18  is mounted on the lower wind speed vertical axis turbine  12  brace system, out of the way of the turbine&#39;s exhaust flow. 
     An embodiment of the invention is shown in greater detail in  FIG. 2 . The lower wind speed turbine  12  includes five blades but it should be understood that more or fewer than five blades may be utilized. The lower wind speed turbine  12  is operatively connected to a motor/generator  20 . The turbine  12  sits above a relatively higher wind speed turbine  14  that is operatively connected to a generator  22 . The higher wind speed turbine  14  is also operatively connected to another generator  24 . In this embodiment, the wind turbines  12  and  14  are supported on a brace  26  that also supports the anemometer  18 . As shown in  FIG. 3 , the output of the motor/generators  20 ,  22  and  24  are delivered to the power electronics (P/E) module  30  and ultimately to a load  32  that may be the electrical grid or an on-site storage system for either local use or as a power reservoir to be either a back-up system or for use at peak demand/peak utility pricing. 
     The five bladed lower wind speed vertical axis wind turbine  12  is designed to start in light winds of, for example, approximately 3 miles per hour and begin producing usable power at, say 5 MPH, producing 40% of generator&#39;s  20  rated capacity. The larger, higher wind speed vertical axis turbine  14  requires a higher start-up torque to operate. For example, the higher wind speed turbine  14  may not start in winds lighter than 8 miles per hour, but once rotating, it can sustain rotation at a lower speed such as 5 miles per hour. Suitable light wind vertical axis wind turbines are available from PacWind, Inc. of Torrance, Calif. See, U.S. Pat. No. 7,109,599 mentioned above. 
     Therefore under this scenario, when the anemometer  18  detects a 5 mile per hour wind speed, electrical energy from the generator  20  (since the lower wind speed turbine  12  is already rotating) is directed to the motor/generator  22  which subsequently starts the turbine  14 . Once the higher wind speed vertical axis turbine  14  is sustainably rotating, electrical energy from both the generator  20  and the generator  22  is distributed to the load  32 . 
     An aid to start-up and braking in an “over-speed” condition may be a pair of Neodymium magnets (not shown) mounted on the turbine  14 &#39;s input and on generator  24 &#39;s output shaft with generator  24 &#39;s magnet wrapped with one or more copper coils connected to the P/E circuit  30 . The Neodymium magnets are positioned to lift turbine  14  off generator  24 &#39;s bearings a few centimeters to reduce the start-up stiction and bearing wear. In an “over-speed” event, the excess current of generator  24  can be switched through the P/E controls to charge the coils wrapping the magnet on generator  24  thereby reversing the magnet&#39;s polarity and acting as an “electric brake” on turbine  14  output shaft until a transient gust has passed, as determined by the anemometer  18 . Anemometer  18  may also “chop” generators  20  and  24 &#39;s variable voltage output being sent to the P/E to not exceed acceptable voltage. The same system will be applied on a smaller scale to turbine  12 &#39;s blades to control its peak torque output. 
     In effect, the smaller turbine  12  and its motor/generator  20  act as a starter motor for the larger, higher wind speed turbine  14 , with the added assistance of the Neodymium magnet system. More importantly, an additional generator  24  is also operatively connected to the higher wind speed turbine  14 . In higher winds or during gusts, the power electronics  30  will engage the third generator  24  at the bottom of the larger unit  14 , creating a third level of counteracting torque against which the turbine blades will engage. This arrangement will thereby serve as both another source of electrical production and, in effect, another electronic “brake” on the turbines&#39; shaft and therefore on the blades&#39; rotational speed. In an “over-speed” event, the excess current of generator  24  can be switched through the P/E controls to charge the coils wrapping the magnet on  24  thereby reversing the magnet&#39;s polarity. This change of polarity acts as an “electric brake” on blade  14 &#39;s output shaft until the transient gust has passed or as a means to lock down the turbine, as determined by anemometer  18 . 
     There are thus three possible load set points (blades of turbines  12  and  14  are scaled to match to local environmental conditions) created by the sizing and choice of the three generators  20 ,  22  and  24 . The three generators effectively create an electronic transmission with three gears sized to: 1) light wind; 2) start up to average geographic wind speed; and 3) maximum wind speed. These three generators  20 ,  22  and  24  are all direct drive units sitting on/under the output shaft, eliminating any output loss that would accompany the use of belts, gears and clutches in conventional transmissions. 
     By using three smaller generators rather than one large generator, the usable power output will start at lower speeds; stay on the power profile of generators found on the market (which have narrow/high rpm power bands for effective conversion to and from mechanical to electrical power); and, be able to produce power in gales and high winds which would cause conventional units either to clip their power output, veer out of the wind, break their unit, or just have to shut down. 
     The blades on the turbines  12  and  14  may be conventional wings or more advanced high lift-to-drag ratio cambered airfoil blades. The tips and connection points of the blades may receive a shape treatment to assist in energy production and lift generation, and the center shaft may be shaped to allow wind flow to pass with minimal disturbance, as would the support structure, brace  26 , which may be composed of one or more supports. 
     If the turbine system of the invention were to be used in, for example, Boston, Mass., the smaller turbine  12  would likely kick in at approximately 3 miles per hour and produce enough power/torque to move the larger bladed unit  14  at a wind speed of 5 miles per hour. At this point, the motor/generator  22  will come on-line and will max out at approximately 13 miles per hour, the average regional wind speed, and continue to generate its maximum voltage/output throughout the generator  24  start and run-up to 29 miles per hour or greater. Above this wind speed, both generators  22  and  24  would likely have their output clipped and maintained at a constant level so as not to damage the power electronics. It should be noted that the three generators  20 ,  22  and  24  may be coupled mechanically on two shafts, one for the light wind generator and one for the larger turbine, coupled with a clutch between a small output shaft and the larger turbine&#39;s shaft, or preferably electrically controlled through the power electronics resulting in a much higher output and broader power band at lower wind speeds than a conventional unit. It is preferred that the units be electrically coupled because a clutch system is both more expensive to manufacture and requires constant monitoring and maintenance and potential failure, leading to catastrophic unit failure. 
     With reference now to  FIG. 4  either one or both of the turbines  12  or  14  may include an auxiliary accelerator blade or airfoil  40  that can swerve into a pre-set angle to the prevailing wind (say 30° to 40° off the wind) by the counter action of an orienting tail  42 . 
     As shown in  FIGS. 5   a  and  5   b , blades  50  and  52  or regions/sections thereof, may contain micro vortex generators  54  or dimples  56  to result in greater extraction of energy from the prevailing wind. 
     It is recognized that modifications and variations of the present invention will be apparent to those of ordinary skill in the art and it is intended that all such modifications and variations be included within the scope of the appended claims.