Abstract:
A wind turbine includes a first vibration sensor for producing a first vibration signal; a second vibration sensor, displaced from the first vibration sensor, for producing a second vibration signal; and a processor for comparing the first vibration signal to the second vibration signal and controlling the wind turbine in response to the comparison.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The subject matter described here generally relates to wind turbines, and, more particularly, to differential vibration sensing and control of wind turbines. 
         [0003]    2. Related Art 
         [0004]    A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by the machinery, such as to pump water or to grind wheat, then the wind turbine may be referred to as a windmill. Similarly, if the mechanical energy is converted to electricity, then the machine may also be referred to as a wind generator or wind power plant. 
         [0005]    Vibrations in various components of a wind turbine may considerably reduce the life of those components and/or lead to early fatigue failures. These vibrations are typically measured with respect to a stationary reference point using accelerometers arranged at critical locations on the components of interest. However, such conventional approaches to vibration sensing do not adequately protect the wind turbine and can lead to unnecessary system shutdown “trips.” 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    These and other drawbacks associated with such conventional approaches are addressed here in by providing, in various embodiments, a wind turbine including a first vibration sensor for producing a first vibration signal; a second vibration sensor, displaced from the first vibration sensor, for producing a second vibration signal; and a processor for comparing the first vibration signal to the second vibration signal and controlling the wind turbine in response to the comparison. Also provided is a method of operating a wind turbine including sensing vibration at a first location on the wind turbine; sensing vibration at a second location on the wind turbine; comparing the sensed vibration at the first location to the sensed vibration at the second location; and controlling the wind turbine in response to an outcome of the comparing step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Various aspects of this technology will now be described with reference to the following figures (“FIGS.”) which are not necessarily drawn to scale, but use the same reference numerals to designate corresponding parts throughout each of the several views. 
           [0008]      FIG. 1  is a schematic side view of a wind generator. 
           [0009]      FIG. 2  is a cut-away orthographic view of the nacelle and huh of the wind generator shown in  FIG. 1 . 
           [0010]      FIG. 3  is an orthographic view of a frame for the nacelle shown in  FIG. 2 . 
           [0011]      FIG. 4  is a schematic control diagram. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  illustrates one example of a wind turbine  2 . This particular configuration for a wind generator type turbine includes a tower  4  supporting a nacelle  6  enclosing a drive train  8 . The blades  10  are arranged on a hub to form a “rotor” at one end of the drive train  8  outside of the nacelle  6 . The rotating blades  10  drive a gearbox  12  connected to an electrical generator  14  at the other end of the drive train  8  along with a control system  16  that may receive input from an anemometer  18 . A first or tower vibration sensor  20  is arranged on the tower  4 , such as near the top of the tower, or at any other location on the tower. Other vibration sensors may also be arranged at other locations on the tower  4  and/or at other locations on the wind turbine  2 . 
         [0013]      FIG. 2  is a cut-away orthographic view of the nacelle  6  and hub  110  of the wind turbine  2  shown in  FIG. 1 . The drive train  8  of the wind turbine  4  (shown in  FIG. 1 ) includes a main rotor shaft  116  connected to hub  110  and the gear box  12 . The control system  16  (in  FIG. 1 ) includes one or more processors, such as microcontrollers  111  within the panel  112 , which provide signals to control the variable pitch blade drive  114  and/or other components of the wind turbine  2 . A high speed shaft (not shown in  FIG. 2 ) is used to drive a first generator  120  via coupling  122 . Various components in the nacelle  6  are be supported by a frame  132 . 
         [0014]      FIG. 3  is an orthographic view of the frame  132  from the nacelle  6  shown in  FIG. 2 . As illustrated in  FIG. 3 , the frame  132  typically includes a main frame, or “bedplate,”  203 , and generator support frame, or “rear frame,”  205  that is typically cantilevered from the bedplate. A second or frame vibration sensor  22  is secured to the frame  132 , such as near the end of the rear frame  205 , for measuring lateral and vertical vibrations. Alternatively, or in addition, other vibration sensors may be secured to other locations on the rear frame  205 , to the bedplate  203 , and/or at other locations on the wind turbine  2 . 
         [0015]    Each of the vibration sensors  20  and/or  22  includes a motion sensor for measuring acceleration, velocity, and/or displacement in one or more dimensions. For example, the vibration sensors  20  and/or  22  may be tri-axial or biaxial, measuring lateral and longitudinal vibrations in the time domain. Other process variables besides vibration, such as displacement, velocity, temperature, and/or pressure, may also be similarly sensed at various turbine locations in a similar manner. The vibration sensors  20  and  22  are arranged to communicate with the control system  16 . For example, the vibrations sensors  20  and  22  may be arranged to communicate with a local or remote processor such as the microcontroller  111  via wired and/or wireless means. 
         [0016]    As illustrated in the schematic control diagram for microcontroller  111  shown in  FIG. 4 , some or all of the vertical and/or lateral outputs from the frame vibration sensor  20  are compared to some or all of the corresponding outputs from the tower vibration sensor  22 . This may be accomplished by a comparator, such as the illustrated adder  24 , or other device, in order to provide a “differential vibration” signal. In the particular example illustrated here, the lateral acceleration signal from the tower vibration sensor  20  is subtracted from the lateral acceleration signal provided by the rear frame vibration sensor  22 . Alternatively, or in addition, the vertical acceleration signal from the tower vibration sensor  20  may subtracted from the vertical acceleration signal provided by the rear frame vibration sensor  22 . Signals on other axes may be compared in a similar manner. 
         [0017]    In this manner, the output signal from the adder  24  is referenced against vibrations sensed in the tower  4  rather than at a stationary reference such as ground. In other words, the cumulative effect of tower vibrations are removed from the output of the adder  24 , so that the signal corresponds more closely to just the vibrations caused by equipment near the rear frame  205 . Relative movement between the tower  4  and frame  205  are therefore more accurately accounted for. Other vibration sensors may also be used so that the output from the second sensor  22 , and/or other sensors, is referenced against vibrations sensed at any other location in the wind turbine  4 . 
         [0018]    A filter  26  may be optionally applied to the signal from the adder  24  in order to exclude frequencies and/or times which are not of interest. However, the filter  26  may also be applied to the signals from other locations, including to the output from the vibration sensors  20  and  22 . Other types of signal processing beside filtering may also be used, such as amplification and/or noise reduction. The “filtered differential vibration signal” from the filter  26  is them sent to an optional adjuster  28  for further processing. For example, the adjuster  28  may be used to calculate a root mean square “RMS” and/or other statistical measure for evaluating whether the “adjusted and filtered differential vibration signal” is within normal operating parameters. The adder  24 , filter  26 , and/or adjuster  28  may be implemented as part of the microcontroller  111  (in  FIG. 2 ) or other processor that is arranged local to or remote from for the wind turbine  2 . 
         [0019]    The differential, filtered differential, and/or adjusted filtered differential signals can then be made at decision point  30  to take further action based upon whether the signal is above a threshold. For example, the adjusted signal may be used to initiate an automatic or manual shutdown “trip” of the wind turbine  2  during periods of excessive vibration when the RMS value rises above a predetermined set point. Such trips may be implemented, for example, by causing variable pitch blade drives  114  to rotate the blades  10  to a feathered position. Other process variables may also be taken into consideration before making a initiating a turbine shut down, or other process change, at decision point  30 . 
         [0020]    In one example where lateral vibration signals from the tower  4  and rear frame  205  were compared in the manner described above, peak vibration amplitudes were reduced 34% and RMS values were reduced 33%. For vertical vibrations, peak vibration amplitudes were reduced 14% and RMS values were reduced 15%. It is therefore expected that, by more accurately measuring the vibration levels at the rear frame  205 , unnecessary turbine shutdowns for excessive vibration may be avoided using the various techniques described above. 
         [0021]    It should be emphasized that the embodiments described above, and particularly any “preferred” embodiments, are merely examples of various implementations that have been set forth here to provide a clear understanding of various aspects of this technology. One of ordinary skill will be able to alter many of these embodiments without substantially departing from scope of protection defined solely by the proper construction of the following claims.