Abstract:
Methods and apparatus of improved windmill design and operation are discussed. An improved windmill assembly includes a support, a movable counterweight and a counterweight position adjuster. The windmill tower experiences oscillations, e.g., oscillations from wind variation, turbulence, varying stress levels, structural design attributes and/or balance considerations. The windmill tower is also subjected to external forces, e.g., a steady state wind pushing the tower in one direction. The windmill assembly includes at least one sensor to measure tower position, tower motion, and/or wind velocity. A computer module, as part of the windmill assembly, processes the sensor output information and uses stored modeling information to determine counterweight position such as to dampen oscillations and/or counteract steady state forces. Control signals are generated and communicated to an actuator to move the counterweight in response to the determination.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is a continuation-in-part of pending allowed U.S. patent application Ser. No. 11/190,687, filed Jul. 27, 2005 the full content of which is hereby expressly incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to alternative energy sources, and more particularly, to methods and apparatus for advanced windmill design.  
       BACKGROUND  
       [0003]     The worldwide appetite for energy has continued to increase as more countries industrialize, and the cost of fossil fuels has also been increasing. There is increased concern with the potential effects of greenhouse gas based global warming. In addition significant safety, security, and environmental issues remain regarding the use of nuclear energy. Therefore, there is a need for improved methods and apparatus for generating energy from clean sources, e.g., wind based energy generation.  
         [0004]     One of the limiting factors of the current generation of wind turbines is the structural ability of the supporting tower to handle the dynamic loads to which it is subjected. Due to variable wind conditions and turbulent wind conditions the loads imposed upon the structure can and, and sometimes do, cause the tower to oscillate. The oscillation and associated bending forces, unless controlled, can cause a premature failure of the structure and induce associated forces and bending loads upon the turbine blades and its support structures.  
         [0005]     Typically, these anticipated forces and associated reactions are taken into account in the determining of the sizing of the turbines and the tower structures. The structure is typically designed to meet worst case events over a specified time interval, e.g., a fifty year cycle, as per current design regulations and criteria. This worst case design, in view of expected worst case anticipated tower oscillation, tends to limit size and power generation levels associated with a particular size structure.  
         [0006]     It would be beneficial if the cost of a windmill assembly structure having a given energy output could be reduced and/or the amount of energy a given size windmill structure can produce could be increased. Methods and apparatus for dampening out and/or limiting tower oscillations would be beneficial. Methods and apparatus to control stress forces within the tower would also be advantageous.  
       SUMMARY  
       [0007]     Various embodiments of the present invention are directed to methods and apparatus that dynamically dampen oscillations within the structure of a windmill assembly. In some embodiments, methods and apparatus of the present invention, by dynamically dampening oscillations, e.g., oscillations experienced by a windmill support tower, limit the oscillations&#39; effect on the structure of the windmill assembly. In various embodiments, controlled repositioning of counterweight is utilized to dampen tower oscillations. Thus, a windmill assembly incorporating an embodiment of the present invention can have reduced initial structural cost over existing designs for the same design level of rated energy output. Alternatively or in addition, a windmill assembly, incorporating an embodiment of present invention, can have increased turbine size over an existing design, for the same initial structural cost. Thus various embodiments of the present invention increase the amount of energy absorption/output per dollar spent on structure.  
         [0008]     In addition to controlling structure oscillations, various embodiments of the present invention, also counteract forces pushing on the tower of the windmill assembly, e.g. by moving a counterweight in an optimal or advantageous position to work to counteract the forces pushing on the tower. For example, the force being counteracted may be a force due to a steady state wind, and the compensation may make the tower lean into the wind to compensate for the wind force, thus allowing the structure to operate in a higher wind than without the leaning capability.  
         [0009]     An exemplary windmill assembly, in accordance with various embodiments of the present invention, includes: a blade assembly, a drive shaft coupled to the blade assembly, a main driveshaft housing for housing at least a portion of the drive shaft, a support tower for supporting the main drive shaft housing, a moveable counterweight, and a counterweight position adjuster for adjusting the position of the counterweight in response to a control signal. In some embodiments, the windmill assembly further includes at least one of a position sensor and a motion sensor mounted on the support tower, e.g., an inertial measurement sensor such as an accelerometer and/or gyroscope. A wind speed sensor is included in some embodiments of the windmill assembly.  
         [0010]     In various embodiments, the windmill assembly includes a computer control module coupled to the at least one sensor and the counterweigh position adjuster, e.g., actuator module. The computer control module generates a counterweight position control signal as a function of at least one received sensor signal. For example, the computer control module can generate a counterweight position control signal to adjust the position of a movable counterweight to dampen tower oscillations detected by the at least one sensor. Alternatively, or in addition, the computer control module can generate a counterweight position control signal to adjust the position of a movable counterweight as a function of measured wind speed from the wind speed sensor, the counterweight position being adjusted to at least partially compensate for force on the support tower due to wind.  
         [0011]     In some embodiments, the counterweight is a sliding weight moved by an actuator, e.g., either toward or away from the turbine. In some embodiments, the counterweight is a hydraulic fluid, and repositioning the counterweight includes pumping at least some fluid from one location to another location. In various embodiments, the computer module includes programs to analyze sensor outputs and determine how far and how fast to move the counterweight and in what direction to dampen a given oscillation. In some embodiments, the computer module also determines the best position of the counterweight for a given wind velocity, e.g., to compensate for a steady state wind condition, and the computer module sends commands to implement the determination. Thus, via computer control, the counterweight, in some embodiments, is positioned towards or away from the turbine to allow for increased absorption of energy from a steady state wind condition similar to a person leaning their weight into the wind so as not to be knocked over.  
         [0012]     An exemplary method of operating a windmill assembly, in accordance with various embodiments of the present invention includes: operating at least one sensor to sense a position of a windmill support tower or motion of the windmill support tower and adjusting the position of a windmill counterweight in response to a signal from the at least one sensor. Another exemplary method of operating a windmill assembly, in accordance with various embodiments includes: operating a wind speed sensor to sense wind speed in the vicinity of the windmill support tower and adjusting the position of a windmill counterweight in response to a signal form the wind speed sensor to adjust the position of a movable counterweight to at least partially compensate for force on the support tower due to wind.  
         [0013]     While various embodiments have been discussed in the summary above, it should be appreciated that not necessarily all embodiments include the same features and some of the features described above are not necessary but can be desirable in some embodiments. Numerous additional features, embodiments and benefits of the various embodiments are discussed in the detailed description which follows. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0014]      FIG. 1  is a drawing including an exemplary windmill assembly implemented in accordance with the present invention.  
         [0015]      FIG. 2  is a drawing of an exemplary computer control module, included as part of the windmill assembly of  FIG. 1 , implemented in accordance with the present invention and using methods of the present invention.  
         [0016]      FIG. 3  is a flowchart of an exemplary method of operating a windmill assembly in accordance with various embodiments of the present invention.  
         [0017]      FIG. 4  is a drawing of a flowchart of an exemplary method of operating a windmill assembly in accordance with various embodiments of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0018]      FIG. 1  is a drawing  100  illustrating an exemplary windmill assembly  102 , implemented in accordance with the present invention, being subjected to gusting winds  104  and turbulent air  106 . Exemplary windmill assembly  102  includes a turbine blade assembly  108 , a support tower  110 , a shaft housing assembly  112 , a computer control module  136 , a wind speed sensor  132 , and a tower motion sensor  134 . Shaft housing assembly  112  includes a main drive shaft, a bearing support assembly  115 , a position indicator  116 , a main dive shaft position detection sensor  118 , a sliding counterweight  120 , a sliding counterweight shaft  122 , a counterweight position sensor  124 , an actuator drive  126 , an actuator support  128 , and a sliding actuator  130 . In addition, wind turbine system  102  includes a wind speed sensor  132  mounted on the shaft housing assembly  112  and a tower motion sensor  134  mounted on the tower  110 . In some embodiments the actuator drive and/or counterweight position sensor are omitted and the counterweight is spring loaded by having springs or other tensioning device attached to the weight so that it tends to remain in a stationary position while the hosing may move due to wind or other turbulence. Thus, while a drive may be employed springs and/or other devices located on one or both sides of the counterweight may also be used to control the counterweight position thereby achieving an oscillation damping effect without the need for a motor to adjust the position of the counterweight used to stabilize the hosing and dampen oscillations.  
         [0019]     The turbine blade assembly  108 , over time, is subjected to winds at various velocities and turbulent air, resulting in different directional stresses at different times. The variation in wind velocity and/or turbulence level can be due to changing weather conditions. In addition, at least some of the turbulence is due a turbine blade/tower mast shadowing effect in region  142 . The presence of the tower  110  causes disruption in air flow in the vicinity of the tower region as the air is forced to flow around the tower mast. The turbine blade assembly  108  is attached to main driveshaft  114  of the shaft housing assembly  112 . Bearing support assembly  115  supports the shaft  114  without the housing  112 . The shaft housing assembly  112  is attached to tower  110 , which tends to move and oscillate as indicated by arrow  140 , e.g., as a function of wind velocity and/or turbulence level. Thus, stresses are transferred into the tower  110  tending to bend and oscillate the tower  110 .  
         [0020]     Wind speed sensor  132  mounted on shaft housing assembly  112  is coupled to computer control module  136 . Wind speed sensor  132  measures wind speed, e.g., the speed of gusting wind  104 , and communicates the measurement information to computer control module  136 , e.g., on an ongoing basis, via signal  146 . Tower motion sensor  134 , e.g., an inertial sensor module, detects transverse and/or angular motion of tower  110 . Motion sensor output signal  144 , output from tower motion sensor  134 , e.g., on an ongoing basis, is received as input by computer control module  136 .  
         [0021]     Position indicator  116 , is attached to main driveshaft  114 , while main drive shaft position detection sensor  118  is attached to shaft housing assembly  112 . Position indicator  116  operating in conjunction with main drive shaft position detection sensor  118  provides output signal  148  to computer control module  136  providing information that can be used to determine when a blade of turbine blade assembly  108  aligns with the tower  110 . In addition, output signal  148  can be used to determine rotational speed of turbine blade assembly  108 . In some embodiments, the position indicator  116 /detection sensor  118  pair is a magnetic field type device, e.g., a Hall effect sensor. In other embodiments, the position indicator  116 /detection sensor  118  pair is an optical type device, e.g., an LED or laser based optical detector module. In still other embodiments, the position indicator  116 /detection sensor  118  pair is an electro-mechanical device, e.g., a lobe or lobes on shaft  114  activating a switch.  
         [0022]     Sliding counterweight  120  can be controllably moved along counterweight shaft  122  in shaft housing assembly  112 . Weight position sensor  124  detects the current position of counterweight  120  and sends counterweight position sensor signal  152  to computer control module  152 .  
         [0023]     Computer control module  136  processes the received sensor information signals  144 ,  146 ,  148  and  152 , and generates actuator drive signal  150  which is communicated to actuator drive  126 . The actuator drive  126  is, e.g., a mechanical or hydraulic motor. Sliding actuator  130 , which is supported by actuator support  128 , is controllable moved by the actuator drive  126  in response to received actuator drive control signal  150 . Controlled motion of sliding actuator  130  causes controlled motion of sliding counterweight  120 . In accordance with the present invention, the placement of and/of motion of the sliding counterweight  120  is controlled such as to reduce oscillations and/or motion of tower  110  and/or reduce stresses between the shaft housing assembly and tower  110 .  
         [0024]     In some embodiments, position indicator  116 /detection sensor  118  and/or weight position sensor  124  are not included. For example, disturbances due to the blade/mast shadowing effect may be determined indirectly through processing of tower motion sensor measurements, and position indicator  116 /main drive shaft position detection sensor  118  may be omitted. As another example, the actuator drive  126 , sliding actuator  130 , and sliding counterweight may have a predetermined known controllable range and weight position sensor is not needed. As still another example, the control loop used for moving the countershaft weight  120  is not concerned with the precise location of the weight  120 , but rather drives the weight  120  along the shaft  122  such as to minimize tower  110  oscillations. In some embodiments, load, e.g., resistance due to power generation, on the main drive shaft  114  is measured and used as an additional input to computer control module  136 .  
         [0025]     In some embodiments, the counterweight is a hydraulic fluid, and a computer control signal controls the pumping of at least some fluid from one location to another to move counterweight. In some embodiments, the counterweight is a multi-part counterweight. In some such embodiments, one part of the counterweight is moved in response to a wind velocity sensor detection signal and another part of the counterweight is moved in response to a tower motion or position detection sensor indication.  
         [0026]      FIG. 2  is a drawing of an exemplary computer control module  136  implemented in accordance with the present invention and using methods of the present invention. Exemplary computer control module  136  includes an interface module  202 , a processor  204 , a network interface  206 , and a memory  208  coupled together via bus  209  over which the various elements interchange data and information. Memory  208  includes routines  210  and data/information  212 . The processor  204 , e.g., a CPU, executes the routines of  210  and uses the data/information  212  in memory  208  to control the operation of the computer control module  136  and windmill assembly  102  and implement methods of the present invention.  
         [0027]     Interface module  202 , e.g., a sensor/actuator interface module, interface to and receives signals from various sensors, e.g., tower motion sensor signal  144 , wind speed sensor signal  146 , main drive shaft position sensor signal  148 , and/or counterweight position sensor signal  152 . Interface module  202  also interfaces to the counterweight actuator drive  126  and sends actuator drive signal  150  to the actuator.  
         [0028]     Network interface  206  couples the computer control module  136  to other network nodes, e.g., a central control node controlling a plurality of wind turbines in the same local vicinity, and/or to the Internet. In some embodiments, at least some of the sensor input information used by computer control module  136  is from sensors located at other sites and/or at least some of the sensor information is communicated via network interface  206 . For example, a wind direction sensor may be located at a nearby site and correspond to a plurality of wind turbine systems in the same local vicinity and its information may be communicated via the Internet and network interface  206 .  
         [0029]     Routines  210  include a sensor information recovery module  214 , an actuator command module  216 , an oscillation damping module  218 , and a steady state balance module  220 . Data/information  212  includes wind speed information  222 , wind direction information  224 , tower motion information  226 , main drive shaft information  228 , counterweight position information  230 , generator load information  232 , stored oscillation model information  234 , stored steady state balance model information  236  and determined counterweight position control information  238 .  
         [0030]     Sensor information recovery module  214  processes signals from various sensors, e.g., tower motion sensor signal, tower position sensor signal, wind speed sensor, counterweight position sensor, shaft position sensor, etc. Oscillating damping module  218 , uses data/information  212  including tower motion information  226  and stored oscillation model information  234  to determine damping adjustments, e.g., determine counterweight positioning control to respond to tower motion sensor detected oscillations. Steady state balance module  220  uses data/information  212  including wind speed information  222  and stored steady state balance model information  236  to determine counterweight balance positioning to respond to steady state or relatively slow time varying conditions, e.g., determine a counterweight position to at least partially compensate for force on the support tower due to wind, e.g., a steady state wind level.  
         [0031]     Actuator command module  216  uses determinations of oscillation damping module  218  and/or steady state balance module  220 , e.g., information  228 , to generate actuator control signals used to reposition the counterweight. Feedback information such as counterweight position information  230  is also utilized by actuator command module  216 .  
         [0032]     Wind speed information  222  includes information from a wind sensor. Wind direction information  224  includes information from a wind direction sensor. Tower motion information  226  includes information from a tower motion sensor and/or tower position sensor. Main drive shaft information  228  includes information from a drive shaft sensor, e.g., shaft position information and/or shaft rate information. Counterweight position information  230  includes countershaft weight sensor information. Generator load information  232  includes information from a sensor measuring output generator load. Determined counterweight position control information  238  includes information determined by oscillation damping module  218  and/or steady state balance module  220 .  
         [0033]     Stored oscillation model information  234  includes information relating anticipated detectable oscillation levels to counterweight repositioning information, e.g., for achieving compensation. Stored steady model information  234  includes information relating anticipated detectable wind speed levels to counterweight repositioning information, e.g., for achieving compensation. In some embodiments, the stored oscillation model information  234  and/or stored steady state balance model information  236  includes an initial predetermined baseline model. In some embodiments, as the windmill assembly operates, the stored models  234  and/or  236  are refined, e.g., with the computer control module  136  performing learning operations to customize model parameters to the particular windmill structure, set of operating conditions, and/or sensors available.  
         [0034]      FIG. 3  is a flowchart of an exemplary method of operating a windmill assembly in accordance with various embodiments of the present invention. The windmill assembly may be exemplary windmill assembly  102  of  FIG. 1 . Operation starts in step  302 , where the windmill system is initialized. Operation proceeds from step  302  to step  304 . In step  304 , the windmill assembly operates at least one sensor to sense a position of a windmill support tower or motion of the windmill support tower. Operation proceeds from step  304  to step  306 . In step  306 , the windmill assembly adjusts the position of a windmill counterweight in response to a signal from said at least one sensor. In some embodiments adjusting the position of the windmill counterweight includes adjusting the counterweight position to dampen windmill support oscillations.  
         [0035]     In step  308 , the windmill assembly operates a wind speed sensor to sense wind speed in the vicinity of the windmill support tower, and then in step  310 , the windmill assembly adjusts the position of the windmill counterweight in response to a signal from said wind speed sensor to adjust the position of the movable counterweight to at least partially compensate for the force on the support tower due to the wind.  
         [0036]     In some embodiments the counterweight is a slidable weight and adjusting the position of the windmill counterweight includes sliding said counterweight, e.g., on a counterweight shaft. In various embodiments, the counterweight is a liquid and adjusting the position of the windmill counterweight includes pumping at least some of said liquid from one location to another. In various embodiments, the counterweight is a multi-part weight. For example, the counterweight may include a plurality of fixed weights and at least one of said plurality of fixed weight may be repositioned without changing the position of at least one other of said plurality of fixed weights. For example, a first repositionable counterweight may be associated with a wind sensor measurement, and a second repositionable counterweight may be associated with a tower motion sensor measurements. As another example, the counterweight may include a first portion which is a fixed solid mass, e.g., a slidable counterweight, and a second portion which is a liquid counterweight. For example, the liquid counterweight portion may be used primarily for a steady state balance level, and the slidable fixed solid mass may be moved to respond to dampen tower oscillations. Different time constants may be associated with the control loops of the two different portions.  
         [0037]     In various embodiments, adjusting the position of the windmill counterweight includes operating a computer module to generate a counterweight position control signal as a function of said at least one sensor. In various embodiments, adjusting the position of the windmill counterweight includes operating a computer module to generate a counterweight position control signal as a function of said at wind speed sensor signal. The computer module, in some embodiments, includes and uses stored oscillation model information, e.g., modeling information relating sensor detected tower oscillation levels and/or profiles to counterweight repositioning control information and/or stored steady state balance model information, e.g., modeling information relating steady state wind speed levels to counterweight repositioning control information.  
         [0038]      FIG. 4  is a drawing of a flowchart  400  of an exemplary method of operating a windmill assembly in accordance with various embodiments of the present invention. The windmill assembly may be exemplary windmill assembly  102  of  FIG. 1 . A computer control module included as part of the windmill assembly may be used for implementing at least some of the steps of the method of flowchart  400 . Operation starts in step  402  where the windmill assembly is powered on and initialized. Operation proceeds from start step  402  to steps  404 ,  406 ,  408 ,  410 ,  412 , and  432  via connecting node A  414 .  
         [0039]     In step  404 , which is performed on a recurring basis, the windmill assembly operates one or support tower sensors of the windmill assembly, the said one or more sensors being responsive to tower position and/or tower position changes. Tower sensor(s) output signals  424  is an output of step  404  and is used as an input in step  434 .  
         [0040]     In some embodiments, at least some or the support tower sensor are mounted on the support tower, e.g., an accelerometer, gyroscope, and/or other inertial measurement instrument attached to the tower. In some embodiments, at least a portion of a support tower sensor assembly is not attached to the tower but is used in detecting tower position and/or tower position changes. For example, a tower position sensor assembly may include a laser beam source and one or more light and/or heat sensitive detection devices, and at least one of the laser beam source and said one or more light and/or heat sensitive detection devices is not located on the tower, e.g., it is located on at a stable site in the vicinity of the tower and is not impacted by wind velocity and/or tower vibration, while the other one of the laser beam source and said light assembly is located on the tower.  
         [0041]     Step  404  includes one or more of sub-steps  416 ,  418 ,  420  and  422 . In sub-step  416 , the windmill assembly operates a motion sensor, e.g., vibration sensor, shock sensor, sway sensor, oscillatory motion sensor, mercury switch sensor, etc., on the support tower to detect motion and output signals. In sub-step  418 , the windmill assembly operates a position sensor, e.g., an encoder, a resolver, a synchro, an optical sensor, a linear position sensor, a GPS module, etc., on the support tower to detect motion information and output signals. In sub-step  420 , the windmill assembly operates an acceleration sensor, e.g., a set of accelerometers on the support tower used to detect acceleration information and output signals, said signals including acceleration information and/or information derived from the measurements, e.g., velocity information and/or position information. In sub-step  422 , the windmill assembly operates a rate sensor, e.g., a rate gyroscope, on the support tower to detect rate information and output signals.  
         [0042]     In step  406 , which is performed on a recurring basis, the windmill assembly operates a wind speed sensor in the vicinity of the windmill assembly to measure wind speed and output wind speed information. Wind speed sensor output signal  426  is an output of step  406  and is used as input in step  434 . In some embodiments wind direction is also measured and utilized in step  434 .  
         [0043]     In step  408 , which is performed on a recurring basis, the windmill assembly operates a drive shaft sensor to detect drive shaft position and/or rate and output information. Drive shaft sensor output signal  428  is an output of step  408  and an input to step  424 . Drive shaft sensor position and/or rate can be useful in determining when a turbine blade will align with the tower and turbine rate of rotation, useful information when attempting to compensate for tower oscillations due to air turbulence and/or vibration balance considerations.  
         [0044]     In step  410 , the windmill assembly operates a counterweight position sensor to detect counterweight position and output information. Counterweight sensor output signal  430  is an output of step  410  and used in step  434  as input. The counterweight position information is advantageous in a closed loop control implementation of the counterweight repositioning.  
         [0045]     In step  412 , which is performed on a recurring basis, the windmill assembly operates a load sensor to detect windmill drive load, e.g., generator load, and output information. Load sensor output signal  432  is an output of step  412  and used as input in step  434 . Different generator loads on the windmill can cause different motion responses at the tower, and such information may be useful in controlling tower motion and/or stresses.  
         [0046]     In step  434 , which is performed on a recurring basis, the windmill assembly determines a desired counterweight position as a function of the received sensor information ( 424 ,  426 ,  428 ,  430 ,  432 ). Step  434  includes sub-steps  436  and  438 . In sub-step  436 , the windmill assembly uses stored model information correlating tower oscillation information to counterweight adjustment information, while in sub-step  438 , the windmill assembly uses stored model information correlation wind speed information, e.g., steady state wind speed information, to counterweight adjustment information. In some embodiments sub-step  436  includes determining oscillatory counterweight positioning control information including at least two of an amplitude value, a frequency value and a phase value.  
         [0047]     Operation proceeds from step  434  to step  438 , in which the windmill assembly generates a counterweight control signal to control repositioning of the counterweight. Then, in step  440 , the windmill assembly sends the generated counterweight control signal to a counterweight positioning device, e.g., an actuator. Operation proceeds from step  440  to step  442 , where the windmill assembly repositions the counterweight in response to a control signal, e.g., moving a sliding counterweight and/or pumping fluid from one location to another. Steps  438 ,  440  and  442  are performed on a recurring basis, e.g. with one iteration being performed in response to an output from step  434 .  
         [0048]     In various embodiments elements described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention. Thus, in some embodiments various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, the present invention is directed to a machine-readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware which may be part of a test device, to perform one or more of the steps of the above-described method(s).  
         [0049]     Numerous additional variations on the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention.