Abstract:
A wind turbine including a rotor, a nacelle, a generator, and a wind sensor is provided, wherein the wind sensor is arranged above a part of the generator that extends between the rotor and the nacelle. Furthermore, a wind farm including a plurality of interconnected wind turbines is described. Yet further, a method of assembling or modifying a wind turbine is described.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European application No. EP 16177526.7 having a filing date of Jul. 1, 2016, the entire contents of which are hereby incorporated by reference. 
       FIELD OF TECHNOLOGY 
       [0002]    The following relates to electrical energy producing devices, in particular to wind turbines. More specifically, the following relates to a wind turbine comprising a rotor, a nacelle, a generator, and a wind sensor. Furthermore, the following relates to a wind farm comprising a plurality of wind turbines. Yet further, the following relates a method of assembling or modifying a wind turbine. 
       BACKGROUND 
       [0003]    Wind speed and wind direction are important parameters for operating a wind turbine. The wind speed is e.g. used to set the load and/or blade angle (pitch) for a wind turbine during operation and the wind direction is used to adjust the direction of the wind turbine relative to the wind (yaw angle). 
         [0004]    Traditionally, the wind parameter values are obtained by means of a wind sensor unit arranged on top of the nacelle as far away from the rotor as possible (i.e. at the rear end of the nacelle) in order to minimize measurement disturbance caused by the rotating rotor blades. To further minimize the measurement disturbance, a filtering of the measurement data may be applied as described in EP 2 515 122 A1. 
         [0005]    However, recent research has revealed that the vortices from the rotor blades, in particular from the root segments of the rotor blades, get wider and wider with increasing downstream distance from the rotor. Thus, the wind reaching the wind sensor unit arranged at the rear upper part of the nacelle is in fact turbulent and not undisturbed by the rotor blades at any time, such that even the above mentioned filtering of the measurement data cannot remove the blade disturbance. Therefore, the obtained values of wind speed and wind direction are in fact not accurate. 
         [0006]    Accordingly, there may be a need for a way of obtaining accurate wind parameter values. 
       SUMMARY 
       [0007]    According to a first aspect of the invention there is provided a wind turbine comprising a rotor, a nacelle, a generator, and a wind sensor, wherein the wind sensor is arranged above a part of the generator that extends between the rotor and the nacelle. 
         [0008]    This aspect of the invention is based on the general idea that the wind sensor is arranged at a position close to the rotor. This is achieved by arranging the wind sensor above a part of the generator that extends between the rotor and the nacelle, i.e. above a rotating part connected to the rotor. Thereby, the wind sensor is positioned close to the rotor. In this position, the disturbances from the blades will be very significant as the blades pass by and much less significant between the blade passes. 
         [0009]    According to an embodiment of the invention, the wind turbine is a direct drive wind turbine. 
         [0010]    In other words, the part of the generator extending between the nacelle and the rotor is a tubular part holding magnets, preferably permanent magnets, on its inner wall, such that the magnets rotate with the rotor and thereby induce electrical currents in a stator part of the generator. 
         [0011]    According to a further embodiment of the invention, the wind turbine further comprises a holding member, wherein the holding member is fastened to the nacelle and holds the wind sensor above the part of the generator that extends between the rotor and the nacelle. 
         [0012]    In other words, the holding member is fastened to and supported by the nacelle in such a way that it is capable of holding the wind sensor in a position above the rotating part of the generator that extends between the rotor and the nacelle. 
         [0013]    According to a further embodiment of the invention, the holding member is fastened to the nacelle by means of one or more beams, in particular by two, three, four or even more beams. 
         [0014]    The at least one beam is preferably made of metal and arranged in such a way that it can maintain the holding member (and the wind sensor arranged thereon) in the desired position relative to the wind turbine during operation. 
         [0015]    Preferably, the beams form a tripod. However, the beam(s) may also form a monopod, a duopod, a quadripod or any other multipod. 
         [0016]    The holding member may preferably be formed as an elongate piece of metal, e.g. steel, with a fastening mechanism for fastening the wind sensor in a central part of the elongate piece. In the case of one beam (monopod), the single beam may be fastened to a central part of the elongate piece. In the case of two beams (duopod), a first beam may be fastened to one end of the elongate piece and a second beam may be fastened to the other end of the elongate piece. In the case of three beams (tripod), a first beam may be fastened to one end of the elongate piece, a second beam may be fastened to the other end of the elongate piece, and a third beam may be fastened to the central part of the elongate piece, e.g. below the wind sensor. 
         [0017]    According to a further embodiment of the invention, the wind sensor is adapted to output a sensor data signal indicative of at least one parameter selected from the group of wind speed and wind direction. 
         [0018]    In other words, the wind sensor is capable of measuring wind speed and/or wind direction. 
         [0019]    The wind sensor may in particular be an anemometer comprising one or more ultrasonic transducers. 
         [0020]    According to a further embodiment of the invention, the wind turbine further comprises an analysis unit adapted to analyze a sensor data signal received from the wind sensor. 
         [0021]    The analysis unit comprises a data processing unit and a memory unit as needed for analyzing the stream of sensor data received during operation. The analysis unit may be a separate dedicated hardware unit or it may be implemented as a software component within the control system of the wind turbine. The sensor data signal preferably comprises digital data, whereby the conversion from analog to digital data may take place within the wind sensor, within the analysis unit or within a separate converting unit. 
         [0022]    The analysis unit preferably outputs relevant parameter values, such as values for wind speed and wind direction, obtained by analyzing the sensor data signal from the wind sensor over a predetermined period of time. 
         [0023]    According to a further embodiment of the invention, the analysis unit is adapted to apply an adaptive filtering algorithm to the sensor data signal in order to reduce influence of rotor blade disturbance. 
         [0024]    More specifically, the adaptive filtering algorithm may be used to detect changes in the sensor signal caused by blade disturbance and to filter out the corresponding parts of the sensor signal. 
         [0025]    According to a further embodiment of the invention, the wind turbine comprises at least one further wind sensor arranged above the part of the generator that extends between the rotor and the nacelle and at a predetermined distance from the wind sensor. 
         [0026]    By having two (or even more) spatially distributed wind sensors, an even more accurate filtering of the respective sensor data may be obtained, e.g. by taking correlation of the sensor signals into consideration. 
         [0027]    According to a second aspect of the invention, there is provided a wind farm comprising a plurality of interconnected wind turbines according to the first aspect or any of the above embodiments thereof. 
         [0028]    According to this aspect of the invention, each wind turbine in the wind farm is capable of accurately measuring local wind parameters, such as wind speed and wind direction. In sum, the wind farm according to this aspect is therefore capable of operating very efficiently. 
         [0029]    According to a third aspect of the invention, there is provided a method of assembling or modifying a wind turbine, in particular a direct drive wind turbine. The method comprises (a) providing a wind turbine comprising a rotor, a nacelle, and a generator, and (b) arranging a wind sensor above a part of the generator that extends between the rotor and the nacelle. 
         [0030]    This aspect of the invention is essentially based on the same idea as the first aspect and the corresponding embodiments described above. More specifically, the method according to the third aspect of the invention allows assembly of a new wind turbine corresponding to the first aspect. Furthermore, the method according to the third aspect also alternatively allows for modification of an existing wind turbine into a wind turbine corresponding to the first aspect. 
         [0031]    It is noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise indicated, in addition to any combination of features belonging to one type of subject matter also any combination of features relating to different subject matters, in particular to combinations of features of the method type claims and features of the apparatus type claims, is part of the disclosure of this document. 
     
    
     
       BRIEF DESCRIPTION 
         [0032]    Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
           [0033]      FIG. 1  shows a wind turbine according an embodiment of the present invention; 
           [0034]      FIG. 2  shows a detailed front view of the wind turbine shown in  FIG. 1 , in accordance with embodiments of the present invention; 
           [0035]      FIG. 3  shows a detailed side view of the wind turbine shown in  FIG. 1 ; 
           [0036]      FIG. 4  shows a detailed upper view of the wind turbine shown in  FIG. 1 , in accordance with embodiments of the present invention; and 
           [0037]      FIG. 5  shows a holding member according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements are provided with the same reference numerals or with reference numerals which differ only within the first digit. 
         [0039]      FIG. 1  shows a wind turbine  100  according an embodiment of the present invention. More specifically, the wind turbine  100  comprises a tower  105  holding a rotor  110 , nacelle  120 , rotating generator part  130 , and a wind sensor  140 . The rotor or hub  110  comprises rotor blades  112 ,  114  and  116 . On top of the nacelle  120 , a platform  122  and a cooling device  124  are arranged as known in the art of direct drive wind turbines. The rotating generator part  130  is arranged between the rotor  110  and the nacelle  120  and is constituted by a tubular member equipped with magnets on its inside wall. The wind sensor  140  is held by a holding member (not shown, see  FIGS. 2 to 5 ). The holding member is fastened to the nacelle  120  by beams  161 ,  162  and  163  in such a way that the wind sensor  140  is held in a position above the rotating generator part  130  between the nacelle  120  and the rotor  110 , i.e. just behind the rotor  110 . 
         [0040]      FIGS. 2 to 4  respectively show a detailed front view, a detailed side view and a detailed upper view of the wind turbine shown  100  in  FIG. 1 . As schematically shown in  FIGS. 2 to 4 , an elongate holding member  150  for holding the wind sensor  140 , here exemplified by sensor devices  142  and  144 , is held in position above the rotating generator part  130  by beams  161 ,  162  and  163 . The beams  161  and  162  extend from respective ends of the elongate holding member  150  to positions towards the respective sides on the upper part of the nacelle  120 . The beam  163  extends between a central part of the elongate holding member  150  and a central part of an upper edge portion of the cooling device  124  of the nacelle  120 . Thereby, the beams  161 ,  162  and  163  form a tripod supporting the holding member in the position above the rotating generator part  130  close to the rotor  110 . 
         [0041]      FIG. 5  shows a holding member  150  according to an embodiment of the present invention, including the embodiment discussed above in conjunction with  FIGS. 1 to 4 . More specifically, the holding member  150  is made of metal and formed as an elongate (i.e. bar-shaped) member having a substantially rectangular cross-section. The elongate holding member  150  comprises end portions  154  and  155  respectively equipped with connecting elements  151  and  152  for connecting with beams  161  and  162  (see  FIGS. 1 to 4 ). The holding member  150  further comprises a central connecting element  153  for connecting with beam  163  (see  FIGS. 1 to 4 ). Furthermore, the holding member  150  comprises a connecting element  156  formed as a stub, i.e. a short tubular piece, for receiving a wind sensor unit (not shown). 
         [0042]    In operation of the wind turbine  100  shown entirely in  FIG. 1  and partially in  FIGS. 2 to 5 , the wind sensor(s)  140 ,  142 ,  144  are positioned above the rotating generator part  120 , i.e. just behind the rotor blades  112 ,  114 ,  116 . Accordingly, the rotating blades  112 ,  114 ,  116  will impact the sensor output signals due to a shadowing effect. The parts (i.e. time segments) of the sensor output signals that are affected by the shadowing effect are preferably identified and disregarded by applying an adaptive filtering algorithm and optimized weighting to the sensor output data, for example as described by Torben Nielsen in “Tracking of Blade Disturbance by Adaptive Filtering and Optimized Weighting of Wind Measurements” (available at http://dx.doi.org/10.18169/PAPDEOTT004946). Thereby, the parts of the sensor signal which are representative of the actual parameter value, such as wind speed or wind direction, and not distorted by blade disturbances are extracted, such that reliable and accurate parameter values can be obtained. 
         [0043]    Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
         [0044]    For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.