Patent Publication Number: US-2007114799-A1

Title: Systems and methods for damping a displacement of a wind turbine tower

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to a wind turbine and more particularly to systems and methods for damping a displacement of a wind turbine tower.  
      Undesired oscillations may occur in a wind turbine tower of a wind turbine used for power generation. Whether the undesired oscillations occur is dependent on a design of the wind turbine tower and a plurality of meteorological conditions.  
      The undesired oscillations may cause a load on the wind turbine tower and other parts of the wind turbine, which may be the cause of fatigue damage and lifetime reduction, as damage in the wind turbine tower slowly grows ultimately leading to a stoppage of the wind turbine. The undesired oscillations also add an uncertainty factor to predictions of effects of the load on the wind turbine.  
     BRIEF DESCRIPTION OF THE INVENTION  
      In one aspect, a method for damping a displacement of a wind turbine tower is provided. The method includes controlling a frequency of oscillation of the wind turbine tower by coupling one of a first beam and a water tank to a plurality of surfaces inside the wind turbine tower.  
      In another aspect, a system for damping a displacement is provided. The system includes a wind turbine tower including a plurality of surfaces, and a processor configured to control a frequency of oscillation of the wind turbine tower by coupling one of a first beam and a water tank to the plurality of surfaces inside said wind turbine tower.  
      In yet another aspect, a wind turbine is provided. The wind turbine includes a wind turbine tower including a plurality of surfaces, a nacelle supported by the wind turbine tower, a wind rotor including at least one blade and coupled to the nacelle, and a processor configured to control a frequency of oscillation of the wind turbine tower by coupling one of a first beam and a water tank to the plurality of surfaces inside the wind turbine tower. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram of an embodiment of a wind turbine.  
       FIG. 2  is a diagram of an embodiment of a system including a nacelle, a tower, and a hub of the wind turbine of  FIG. 1 .  
       FIG. 3  is a diagram of another embodiment of a wind turbine.  
       FIG. 4  is a diagram of yet another embodiment of a wind turbine.  
       FIG. 5  is a graph illustrating an effect of wind on a prior art wind turbine tower that does not include a beam.  
       FIG. 6  is a graph illustrating an effect of wind on the tower of the wind turbine of  FIG. 1  when the tower includes the beam.  
       FIG. 7  is a diagram of an embodiment of a wind turbine.  
       FIG. 8  is a diagram of another embodiment of a wind turbine.  
       FIG. 9  is an embodiment of a system for damping a displacement of the tower of  FIG. 1 .  
       FIG. 10  is another embodiment of a system for damping a displacement of the tower of  FIG. 1 .  
       FIG. 11  is another embodiment of a system for damping a displacement of the tower of  FIG. 1 .  
       FIG. 12  is yet another embodiment of a system for damping a displacement of the tower of  FIG. 1 .  
       FIG. 13  is still another embodiment of a system for damping a displacement of the tower of  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  is a diagram of an embodiment of a wind turbine  100 . Wind turbine  100  includes a nacelle  102 , a tower  104 , a rotor  106  having at least one rotor blade  108  and a rotating hub  110 . Examples of tower  104  include a lattice tower and a tubular tower. Nacelle  102  is mounted atop tower  104 , a portion of which is shown in  FIG. 1 . Rotor blades  108  are attached to hub  110 .  
       FIG. 2  is a diagram of an embodiment of a system  111  including nacelle  102 , tower  104 , and hub  110 . Nacelle  102  houses a control panel  112  including a processor  113 . As used herein, the term processor is not limited to just those integrated circuits referred to in the art as a processor, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller, an application specific integrated circuit, and any other programmable circuit.  
      Hub  110  includes a variable blade pitch drive  114 . Nacelle  102  also houses a portion of main rotor shaft  116 , a gear box  118 , a generator  120 , and a coupling  122 . A yaw drive  124  and a yaw deck  126  are housed within nacelle  102 . A meteorogical boom  128  is coupled to nacelle  102 . Nacelle  102  further houses a main bearing  130  and a main frame  132 . Processor  113  controls rotor  106  and components housed within nacelle  102 . In an alternative embodiment, processor  113  is located within tower  104  and another processor is located within control panel  112 . The other processor controls rotor  106  and components housed within nacelle  102 . The other processor communicates with processor  113 .  
      Variable blade pitch drive  114  is provided to control a pitch of blades  108  that drive hub  110  as a result of wind. In an alternative embodiment, a plurality of pitches of blades  108  are individually controlled by blade pitch drive  114 .  
      Main rotor shaft  116 , which is a low speed shaft, is connected to hub  110  via main bearing  130  and is connected at an opposite end of shaft  116  to gear box  118 . Gear box  118  utilizes a dual path geometry to drive an enclosed high speed shaft operating at a higher speed than main rotor shaft  116 . Alternatively, main rotor shaft  116  is coupled directly to generator  120 . The high speed shaft is used to drive generator  120 , which is mounted on main frame  132 . A torque of rotor  106  is transmitted via coupling  122  to generator  120 .  
      Yaw drive  124  and yaw deck  126  provide a yaw orientation system for wind turbine  100 . Meterological boom  128  provides information for processor  113  in control panel  112 , and the information includes wind direction and/or wind speed. Examples of wind direction includes a left-to-right direction and a right-to-left direction.  
       FIG. 3  is a diagram of an embodiment of a wind turbine  200 , which is an example of wind turbine  100 . Wind turbine  200  includes hub  10 , rotor blades  108 , nacelle  102 , a tower  202 , an oscillation sensor  204 , and a plurality of drivers  206 ,  208 ,  210 , and  212 . Tower  202  is a tubular steel tower and is an example of tower  104 . One example of oscillation sensor  204  includes an accelerometer. Drivers  206 ,  208 ,  210 , and  212  are located inside tower  202 . In an alternative embodiment, drivers  206 ,  208 ,  210 , and  212  are located within nacelle  102 . Tower  202  is coupled to a plurality of shock absorbers  214 ,  216 ,  218 , and  220 , and a plurality of beams  222  and  224 . Beams  222  and  224  are made of a metal, such as stainless steel and/or carbon steel. An example of any of shock absorbers  214 ,  216 ,  218 , and  220  includes a hydraulic cylinder. In an alternative embodiment, tower  202  is coupled to more than four shock absorbers  214 ,  216 ,  218 , and  220 . In yet another alternative embodiment, tower  202  is coupled to more than two beams  222  and  224 .  
      Beam  222  is coupled to an inside surface  226  of tower  202  via shock absorber  216  and is coupled to an inside surface  228  of tower  202  via shock absorber  218 . As an example, beam  222  is attached, such as riveted and/or clamped, to shock absorbers  216  and  218 . As another example, shock absorber  216  is clamped to inside surface  226  and shock absorber  218  is clamped to inside surface  228 . Beam  224  is coupled to inside surface  226  of tower  202  via shock absorber  214  and is coupled to inside surface  228  of tower  202  via shock absorber  220 . As an example, beam  224  is attached, such as riveted and/or clamped, to shock absorbers  214  and  220 . As another example, shock absorber  214  is clamped to inside surface  226  and shock absorber  220  is clamped to inside surface  228 . In an alternative embodiment, tower  202  is coupled to shock absorbers  214  and  220  and beam  224  but is not coupled to shock absorbers  216  and  218  and beam  222 . In another alternative embodiment, tower  202  is coupled to shock absorbers  216  and  218  and beam  222  but is not coupled to shock absorbers  214  and  220  and beam  224 . Oscillation sensor  204  is coupled to a surface, such as inside surface  228  or alternatively an outside surface  230 , of tower  202 .  
      Meteorogical conditions, such as wind, create oscillations in tower  202 . Oscillation sensor  204  senses the oscillations to generate an electrically sensed signal  232 . Processor  113  receives electrically sensed signal  232  as an input and includes a frequency converter, such as a Fourier transform device, to determine an oscillation frequency of electrically sensed signal  232 . Processor  113  further determines whether the oscillation frequency of electrically sensed signal  232  is within a range of an eigenfrequency of the oscillations of tower  202 . The range of the eigenfrequency depends on a height of tower  104  and a resistance of tower  104  to a force of wind. An example of the range includes a number of oscillations of tower  104  that span 1.5 meters in a first direction and 1.5 meters in a second direction opposite to the first direction per second. The span is measured at a top portion, such as nacelle  102 , of tower  104 . Another example of the range includes 5-10 oscillations per minute, where each oscillation spans a distance 1.5 meters in the first direction at the top portion and 1.5 meters in the second direction at the top portion. If processor  113  determines that the oscillation frequency is within the range of the eigenfrequency, processor  113  controls at least one of shock absorbers  214 ,  216 ,  218 , and  220  via at least one of corresponding drivers  206 ,  208 ,  210 , and  212  to damp the oscillation frequency until the oscillation frequency is outside the range of the eigenfrequency. If processor  113  determines that the oscillation frequency is outside the range of eigenfrequency, processor  113  does not control shock absorbers  214 ,  216 ,  218 , and  220 .  
      Processor  113  controls at least one of shock absorbers  214 ,  216 ,  218 , and  220  via at least one of corresponding drivers  206 ,  208 ,  210 , and  212  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to a plane of rotor blades  108 , processor  113  controls at least one of shock absorbers  214  and  220  to decrease a length of beam  224 . As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  controls at least one of shock absorbers  216  and  218  to decrease a length of beam  222 . As yet another example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  controls at least one of shock absorbers  214  and  220  to decrease a length of beam  224  and controls at least one of shock absorbers  216  and  218  to increase a length of beam  222 . As still another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  controls at least one of shock absorbers  214  and  220  to increase a length of beam  224  and controls at least one of at least one of shock absorbers  216  and  218  to decrease a length of beam  222 .  
       FIG. 4  is a diagram of an embodiment of a wind turbine  250 , which is an example of wind turbine  100 . Wind turbine  250  includes hub  110 , rotor blades  108 , nacelle  102 , and a tower  252 . Tower  252  is a lattice tower made of a plurality of steel legs  254 ,  256 ,  258 , and  260 , and a plurality of welded steel profiles  262 . Tower  250  is an example of tower  104 . Tower  250  is coupled to shock absorbers  214 ,  216 ,  218 , and  220 , and beams  222  and  224 . Alternatively, tower  250  is coupled to more than four shock absorbers  214 ,  216 ,  218 , and  220 . In yet another alternative embodiment, tower  202  is coupled to more than two beams  222  and  224 .  
      Beam  222  is coupled to leg  254  via shock absorber  216  and to leg  260  via shock absorber  218 . As an example, beam  222  is attached, such as riveted and/or clamped, to shock absorber  218  and shock absorber  218  is clamped to leg  260 . As yet another example, beam  222  is attached, such as riveted and/or clamped, to shock absorber  216  and shock absorber  216  is clamped to leg  254 . Beam  224  is coupled to leg  256  via shock absorber  220  and to leg  258  via shock absorber  214 . As an example, beam  224  is attached, such as riveted and/or clamped, to shock absorber  220  and shock absorber  220  is clamped to leg  256 . As yet another example, beam  224  is attached, such as riveted and/or clamped, to shock absorber  214  and shock absorber  214  is clamped to leg  258 . Oscillation sensor  204  is attached to any one of steel profiles  262 . Optionally, oscillation sensor  204  is attached to any one of legs  254 ,  256 ,  258 , and  260 .  
      When the meteorogical conditions create the oscillations in tower  252 , processor  113  controls at least one of shock absorbers  214 ,  216 ,  218 , and  220  to damp the oscillation frequency in a similar manner described above with reference to  FIG. 3 .  
       FIG. 5  is a graph illustrating an effect of wind on a prior art wind turbine tower that does not include beams  222  and  224  ( FIG. 4 ). Wind speed is plotted on a y-axis  302  and time is plotted on an x-axis  304 . A plot  306  shows a wind speed with respect to time and a plot  308  shows a displacement, such as the oscillations, of the prior art wind turbine tower. The oscillations of the prior art wind turbine tower are not damped.  
       FIG. 6  is a graph illustrating an effect of wind on tower  104  ( FIG. 1 ) that includes at least one of beams  222  and  224  ( FIG. 3 ). A plot  310  shows a displacement, such as the oscillations, of tower  104  with respect to time. It is noted that tower  104  experiences lesser displacement than the displacement experienced by prior art wind turbine towers.  
       FIG. 7  is a diagram of an embodiment of wind turbine  200  in which a water tank  352  is coupled to tower  202 . A surface  354  of water tank  352  is attached, such as clamped and/or riveted, to inside surface  226  of tower  202 . Another surface  356 , located opposite to surface  354 , of water tank  352  is also attached, such as clamped or riveted, to inside surface  228  of tower  202 . Alternatively, surface  354  of water tank  352  is attached to inside surface  226  of tower  202  via at least one of beams  402  and  404  (shown in  FIG. 8 ) made of metal, such as stainless steel and/or carbon steel. Surface  356  of water tank  352  is also attached to inside surface  228  of tower  202  via at least one of beams  406  and  408  (shown in  FIG. 8 ) made from the metal. Beams  402  and  404  are attached, such as clamped and/or riveted, to surface  354  of water tank  352  and also attached, such as clamped and/or riveted, to inside surface  226 . Beams  406  and  408  are attached, such as clamped and/or riveted, to surface  356  of water tank  352  and also attached, such as clamped and/or riveted, to inside surface  228 .  
       FIG. 8  is a diagram of an embodiment of wind turbine  250 . Surface  354  of water tank  352  is attached, such as clamped and/or riveted, to beams  402  and  404  and surface  356  of water tank  352  is attached, such as clamped and/or riveted, to beams  406  and  408 . Beam  402  is attached, such as clamped and/or riveted, to leg  258  and beam  404  is attached, such as clamped and/or riveted, to leg  254 . Moreover, beam  406  is attached, such as clamped and/or riveted, to leg  256  and beam  408  is attached, such as clamped and/or riveted, to leg  260 . In an alternative embodiment, beam  402  is attached to one of steel profiles  262  coupled to legs  254  and  258  and beam  404  is also attached to another one of steel profiles  262  coupled to legs  254  and  258 . In yet another alternative embodiment, beam  406  is attached to one of steel profiles  262  coupled to legs  256  and  260  and beam  408  is also attached to another one of steel profiles  262  coupled to legs  256  and  260 .  
       FIG. 9  is an embodiment of a system  450  for damping a displacement of tower  100 . System  450  includes water tank  352 , a plurality of containers  452  and  454 , processor  113 , and oscillation sensor  204 . Containers  452  and  454  are located within water tank  352 . Container  452  includes a flow restriction valve  456  and container  454  includes a flow restriction valve  458 . Container  452  is attached to an inside surface  460  of water tank  352 . For example, container  452  is attached, such as clamped and/or riveted, to a metal rod that is attached, such as clamped and/or riveted, to inside surface  460 . Container  454  is also attached to an inside surface  462  of water tank  352 . For example, container  454  is attached, such as clamped and/or riveted, to a metal rod that is attached, such as clamped and/or riveted, to inside surface  462 . Containers  452  and  454  are located on opposite sides of a center of a bottom side  464  of water tank  352 . A perpendicular distance  466  between an outside surface  468  of container  452  and inside surface  460  of water tank  352  is equal to a perpendicular distance  470  between an outside surface  472  of container  452  and an outside surface  474  of container  454 . Outside surfaces  468  and  472  are located on opposite sides of flow restriction valve  456 . Perpendicular distance  466  is also equal to a perpendicular distance  476  between an outside surface  478  of container  454  and inside surface  462  of water tank  352 . Outside surfaces  474  and  478  are located on opposite sides of flow restriction valve  458 . In an alternative embodiment, perpendicular distance  466  is unequal to at least one of distances  470  and  476 . Water tank  352  includes water  480 . In an alternative embodiment, system  450  does not include one of containers  452  and  454 .  
      Oscillation sensor  204  senses the oscillations to generate electrically sensed signal  232 . Processor  113  receives electrically sensed signal  232  as an input and determines whether the oscillations are within the range of the eigenfrequency. If processor  113  determines that the oscillations are within the range, processor  113  controls at least one of flow restriction valves  456  and  458  via at least one of drivers  206  and  208  to damp the oscillation frequency until the oscillation frequency is outside the range of the eigenfrequency. If processor  113  determines that the oscillation frequency is outside the range, processor  113  does not control flow restriction valves  456  and  458 .  
      Processor  113  controls at least one of flow restriction valves  456  and  458  via at least one of drivers  206  and  208  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens flow restriction valve  458  and does not open flow restriction valve  456 . When flow restriction valve  458  opens, water from water tank  352  flows into container  454  via flow restriction valve  458  until a level of water inside container  454  is equal to a level of water inside water tank  352 . Processor  113  opens flow restriction valve  458  until the oscillation frequency is outside the range of the eigenfrequency. Processor  113  closes flow restriction valve  458  upon determining that the oscillation frequency is outside the range. As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens flow restriction valve  456  and does not open flow restriction valve  458 . When flow restriction valve  456  opens, water from water tank  352  flows into container  452  via flow restriction valve  456  until a level of water inside container  452  is equal to a level of water inside water tank  352 . Processor  113  opens flow restriction valve  456  until the oscillation frequency is outside the range of the eigenfrequency. Processor  113  closes flow restriction valve  456  upon determining that the oscillation frequency is outside the range.  
      In an alternative embodiment, processor  113  simultaneously controls flow restriction valves  456  and  458  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens flow restriction valve  458  faster than flow restriction valve  456 . Processor  113  opens flow restriction valves  456  and  458  until the oscillation frequency is outside the range. Processor closes valves  456  and  458  upon determining that the oscillation frequency is outside the range. As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens flow restriction valve  456  faster than flow restriction valve  458 .  
       FIG. 10  is a diagram of an embodiment of a system  500  for damping a displacement of tower  100 . System  500  includes water tank  352 , container  452  with a lid  502  and flow restriction valve  456 , container  454  with a lid  504  and flow restriction valve  458 , drivers  206 ,  208 ,  210 , and  212 , a driver  506 , oscillation sensor  204 , processor  113 , and an air pressure pump  508 . Lid  502  includes an air flow valve  510  and lid  504  includes an air flow valve  512 . An example of air pressure pump  508  includes an air compressor. Lid  502  is attached, such as welded, to container  452  and lid  504  is also attached, such as welded, to container  454 . A lid  514  is also attached, such as welded, to water tank  352 . In an alternative embodiment, system  500  includes container  452  with lid  502  and does not include container  454  with lid  504 . In another alternative embodiment, system  500  includes container  454  with lid  504  and does not include container  452  with lid  502 .  
      Oscillation sensor  204  senses the oscillations to generate electrically sensed signal  232 . Processor  113  receives electrically sensed signal  232  as an input and determines whether the oscillations are within the range of the eigenfrequency. If processor  113  determines that the oscillations are within the range, processor  113  controls at least one of flow restriction valve  456  via driver  206 , flow restriction valve  458  via driver  208 , air pressure pump  508  via driver  506 , air flow valve  510  via driver  210 , and air flow valve  512  via driver  212  to damp the oscillation frequency until the oscillation frequency is outside the range of the eigenfrequency. If processor  113  determines that the oscillation frequency is outside the range, processor  113  does not control flow restriction valves  456  and  458 , air pressure pump  508 , and air flow valves  510  and  512 .  
      Processor  113  controls at least one of flow restriction valve  456 , flow restriction valve  458 , air pressure pump  508 , air flow valve  510 , and air flow valve  512  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  512  and does not open air flow valve  510 . When air flow valve  512  opens, air from water tank  352  flows into container  454  via air flow valve  512  until a pressure of air inside container  454  is equal to a pressure of air inside water tank  352 . Processor  113  opens air flow valve  512  until the oscillation frequency is outside the range of the eigenfrequency. Processor  113  closes air flow valve  512  upon determining that the oscillation frequency is outside the range. As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  510  and does not open air flow valve  512 . When air flow valve  510  opens, air from water tank  352  flows into container  452  via air flow valve  510  until a pressure of air inside container  452  is equal to a pressure of air inside water tank  352 . Processor  113  opens air flow valve  510  until the oscillation frequency is outside the range of the eigenfrequency. Processor  113  closes air flow valve  510  upon determining that the oscillation frequency is outside the range.  
      Processor  113  energizes air pressure pump  508  via driver  506  to provide compressed air and to increase a pressure of air inside water tank  352  until the oscillation frequency is within the range. An increase in pressure inside water tank  352  results in an increase in pressure in container  452  when air flows from water tank  352  into container  452  via air flow valve  510 . Similarly, an increase in pressure inside water tank  352  results in an increase in pressure in container  454  when air flows from water tank  352  into container  454  via air flow valve  512 . Processor  113  deenergizes pump upon determining that the oscillation frequency is outside the range.  
      In an alternative embodiment, processor  113  simultaneously controls at least two of flow restriction valve  456 , flow restriction valve  458 , air flow valve  510 , air flow valve  512 , and air pressure pump  508  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  512  and flow restriction valve  458  faster than air flow valve  510  and flow restriction valve  456 . Processor  113  opens air flow valve  512  and flow restriction valve  458  until the oscillation frequency is outside the range. Processor  113  closes air flow valve  512  and flow restriction valve  458  upon determining that the oscillation frequency is outside the range. As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  510  and flow restriction valve  456  faster than flow restriction valve  458  and air flow valve  512 . As yet another example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  512  and flow restriction valve  458  without opening air flow valve  510  and flow restriction valve  456 . As still another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  510  and flow restriction valve  456  without opening flow restriction valve  458  and air flow valve  512 .  
      As another example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  512 , flow restriction valve  458 , and air flow valve  510 , and does not open flow restriction valve  456 . Processor  113  opens air flow valve  512 , flow restriction valve  458 , and air flow valve  510  until the oscillation frequency is outside the range. Processor  113  closes air flow valves  510  and  512  and flow restriction valve  458  upon determining that the oscillation frequency is outside the range. As yet another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  510 , flow restriction valve  456 , and air flow valve  512  and does not open flow restriction valve  458 . Processor  113  opens air flow valve  510 , flow restriction valve  456 , and air flow valve  512  until the oscillation frequency is outside the range. Processor  113  closes air flow valve  510 , flow restriction valve  456 , and air flow valve  512  upon determining that the oscillation frequency is outside the range.  
      As another example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  13  opens air flow valve  512 , flow restriction valve  458 , and air flow valve  510  faster than flow restriction valve  456 . Processor  113  opens air flow valve  512 , flow restriction valve  458 , air flow valve  510 , and flow restriction valve  456  until the oscillation frequency is outside the range. Processor closes air flow valve  512 , flow restriction valve  458 , air flow valve  510 , and flow restriction valve  456  upon determining that the oscillation frequency is outside the range. As yet another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens air flow valve  510 , flow restriction valve  456 , and air flow valve  512  faster than flow restriction valve  458 . Processor  113  opens air flow valve  510 , flow restriction valve  456 , and air flow valve  512 , and flow restriction valve  458  until the oscillation frequency is outside the range. Processor closes air flow valve  510 , flow restriction valves  456  and  458 , and air flow valve  512  upon determining that the oscillation frequency is outside the range.  
      Processor  113  controls air pressure pump  508  via driver  506  by either energizing air pressure pump  508  or deenergizing air pressure pump  508 . Processor  113  simultaneously controls air pressure pump  508  while controlling at least one of air flow valve  510 , flow restriction valve  456 , flow restriction valve  458 , and air flow valve  512 . In an alternative embodiment, processor  113  does not control air pressure pump  508  while simultaneously controlling at least one of air flow valve  510 , flow restriction valve  456 , flow restriction valve  458 , and air flow valve  512 .  
       FIG. 11  is an embodiment of a system  550  for damping a displacement of tower  100 . System  550  includes water tank  352 , container  452  with flow restriction valve  456 , container  454  with flow restriction valve  458 , drivers  206 ,  208 ,  210 ,  212 , and  506 , oscillation sensor  204 , processor  113 , and a plurality of hydraulic cylinders  552 ,  554 , and  556 . Hydraulic cylinder  552  includes a piston  558  and a housing  560 , hydraulic cylinder  554  includes a piston  562  and a housing  564 , and hydraulic cylinder  556  includes a piston  566  and a housing  568 . Piston  558  includes a piston head  570 , piston  562  includes a piston head  572 , and piston  566  includes a piston head  574 . Piston head  570  seals perpendicular distance  466  ( FIG. 9 ), piston head  572  seals perpendicular distance  470  ( FIG. 9 ), and piston head  574  seals perpendicular distance  476  ( FIG. 9 ). In an alternative embodiment, system  550  does not include all of hydraulic cylinders  552 ,  554 , and  556 .  
      Oscillation sensor  204  detects the oscillations to generate electrically sensed signal  232 . Processor  113  receives electrically sensed signal  232  as an input and determines whether the oscillations are within the range of the eigenfrequency. If processor  113  determines that the oscillations are within the range, processor  113  controls at least one of flow restriction valve  456  via driver  206 , flow restriction valve  458  via driver  208 , hydraulic cylinder  552  via driver  506 , hydraulic cylinder  554  via driver  210 , and hydraulic cylinder  556  via driver  212  to damp the oscillation frequency until the oscillation frequency is outside the range of the eigenfrequency. If processor  113  determines that the oscillation frequency is outside the range, processor  113  does not control flow restriction valves  456  and  458 , and hydraulic cylinders  552 ,  554 , and  556 .  
      Processor  113  controls at least one of hydraulic cylinders  552 ,  554 , and  556  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  controls piston  558  to protrude and apply force in a downward direction pointing towards bottom surface  464 , and controls at least one of pistons  562  and  566  to withdraw and reduce force in the downward direction. As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  controls piston  566  to protrude and apply force in the downward direction, and controls at least one of pistons  558  and  562  to withdraw and reduce force in the downward direction. As yet another example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  controls piston  556  to increase applying force in the downward direction at a rate faster than that of a decrease in force in the downward direction by pistons  562  and  566 . As still another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  controls piston  566  to increase applying force in the downward direction at a rate faster than that of an increase in force in the downward direction by pistons  558  and  562 .  
      In an alternative embodiment, processor  113  simultaneously controls at least two of flow restriction valve  456 , flow restriction valve  458 , hydraulic cylinder  552 , hydraulic cylinder  554 , and hydraulic cylinder  556  to damp the oscillation frequency. For example, if wind is blowing in the left-to-right direction perpendicular to the plane of rotor blades  108 , processor  113  opens flow restriction valve  458 , does not open flow restriction valve  456 , controls piston  558  to apply force in the downward direction, and controls at least one of pistons  562  and  566  to reduce force in the downward direction. As another example, if wind is blowing in the right-to-left direction perpendicular to the plane of rotor blades  108 , processor  113  opens flow restriction valve  456 , does not open flow restriction valve  458 , controls piston  566  to apply force in the downward direction, and controls at least one of pistons  558  and  562  to reduce force in the downward direction.  
       FIG. 12  is an embodiment of a system  600  for damping a displacement of tower  100 . System  600  includes processor  113 , a voltage source  602 , such as a direct current voltage source, a triac  604 , and a valve  606 . Triac  604  is an example of any of driver  206 , driver  208 , driver  210 , driver  212 , and driver  506  ( FIG. 11 ). Valve  606  is an example of any of flow restriction valve  456 , flow restriction valve  458 , air flow valve  510 , and air flow valve  512  ( FIG. 10 ). Valve  606  includes a solenoid  608 , a valve body  610 , and a spring  612 .  
      Processor  113  receives electrically sensed signal  232  and includes an analog-to-digital converter that converts electrically sensed signal  232  from an analog format to a digital format. Based upon electrically sensed signal  232 , processor  113  determines to control valve  606 . Processor  113  controls valve  606  by transmitting a processor output signal  614  to triac  604 . Triac  604  turns on and generates a triac output signal  616  upon determining that processor output signal  614  is above a threshold of triac  604 . Solenoid  608 , upon receiving triac output signal  616 , generates an electromagnetic field that forces valve body  610  towards an open end of valve  606  and against a force of spring  612 . The open end of valve  606  is open to an environment outside valve  606 . Motion of valve body  610  against a force of spring  612  compresses spring  612  and opens valve  606  to the environment located outside valve  606 .  
      Based upon electrically sensed signal  232 , processor  113  determines not to control valve  606  and does not transmit processor output signal  614 . Upon a non-receipt of processor output signal  614 , triac  604  determines that processor output signal  614  is below the threshold of triac  605 , turns off, and does not generate triac output signal  616 . Solenoid  608 , upon non-receipt of triac output signal  616 , does not generate the electromagnetic field and spring  612  expands. The expansion of spring  612  closes valve  606  by forcing valve body  610  towards a closed end of valve  606 . The closed end of valve  606  is not open to the environment outside valve  606 .  
       FIG. 13  is an embodiment of a system  650  for damping a displacement of tower  100 . System  650  includes processor  113 , voltage source  602 , valve  606 , an NPN bipolar junction transistor (BJT)  652 , and a hydraulic cylinder  654 . Hydraulic cylinder  654  is an example of any of shock absorber  214 , shock absorber  216 , shock absorber  218 , shock absorber  220 , hydraulic cylinder  552 , hydraulic cylinder  554 , and hydraulic cylinder  556  ( FIGS. 4 and 11 ). NPN BJT  652  is an example of any of driver  206 , driver  208 , driver  210 , driver  212 , and driver  506  ( FIG. 11 ). In an alternative embodiment, a PNP BJT or alternatively a field effect transistor (FET) is used instead of NPN BJT  652 . Hydraulic cylinder  654  includes a housing  656  and a piston  658  including a piston head  660 . Housing  656  includes spring  612 . Housing  656  is an example of any of housing  560 , housing  564 , and housing  568  ( FIG. 11 ). Piston  658  is an example of any of piston  558 , piston  562 , and piston  566  ( FIG. 11 ). Piston head  660  is an example of any of piston head  570 , piston head  572 , and piston head  574  ( FIG. 11 ). Housing  656  includes a hole that is drilled and threaded. A hose  660  is inserted in the hole. The hole provides an inlet for insertion of oil into housing  656 . The hole also provides an outlet to oil that is within housing  656 . Housing  656  also includes another hole to provide an inlet and an outlet to air.  
      Based upon electrically sensed signal  232 , processor  113  controls valve  606  by transmitting processor output signal  614  to NPN BJT  652 . NPN BJT  652  turns on and generated a BJT output signal  664  upon determining that processor output signal  614  is above a threshold of NPN BJT  652 . Valve  606  opens upon receiving BJT output signal  664  and allows oil to flow from a reservoir via hose  662  to housing  656 . The flow of oil via hose  662  into housing  656  causes piston head  660  to apply a force in a direction, such as the downward direction, the left-to-right direction, and the right-to-left direction, to compress spring  612 . Application of force against  612  decreases a length of any of beams  222  and  224  ( FIG. 4 ).  
      Based upon electrically sensed signal  232 , processor  113  does not control hydraulic cylinder  654  and does not transmit processor output signal  614 . Upon a non-receipt of processor output signal  614 , NPN BJT  652  determines that processor output signal  614  is below the threshold of NPN BJT  652 , turns off, and does not generate BJT output signal  664 . Valve  606  is closed upon non-receipt of BJT output signal  664  and oil stops flowing from the reservoir to housing  656  via valve  606 . Spring  612  expands when valve  606  is closed. The expansion of spring withdraws piston head  660  and reduces force in a direction, such as the downward direction, right-to-left direction, and the left-to-right direction. Reduction in force against spring  612  increases a length of any of beams  222  and  224  ( FIG. 4 ).  
      It is noted that a driver driving a device, is not included within a system if the device is not included within the system. For example, if lid  502  with air flow valve  510  is not included within system  500  ( FIG. 10 ), driver  210  is not included within system  500 .  
      Technical effects of the systems and methods for damping a displacement of wind turbine tower  100  include damping the oscillation frequency until the oscillation frequency is outside the range of the eigenfrequency. Damping of the oscillation frequency is achieved by making tower  100  oscillate in a direction of wind. For example, if wind oscillates in the left-to-right direction, tower  100  is controlled by processor  113  to oscillate in the left-to-right direction. As another example, if wind oscillates in the right-to-left direction, tower  100  is controlled by processor  113  to oscillate in the right-to-left direction.  
      While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.