Patent Publication Number: US-2010117368-A1

Title: Drive train supporting structure for a wind turbine

Description:
BACKGROUND 
     The present disclosure generally relates to wind turbines adapted for converting mechanical wind energy into electrical output energy, and in particular relates to a drive train supporting structure for a wind turbine. 
     A drive train of a wind turbine typically includes a rotor having a plurality of rotor blades, a hub, a speed adapter unit or a gear box and a generator. Typically, the supporting structure for said drive train is greatly contributes to the overall weight of an upper part of the wind turbine. During the operation of the wind turbine, e.g. when the rotor having the plurality of rotor blades is rotating, vibrations might occur. 
     Typically, the rotor rotates about a main axis which is oriented horizontally wherein the tilt, e.g. the horizontal orientation of the main axis of the rotor, cannot be changed. In order to adapt operation parameters of the wind turbine to environmental conditions, a yawing angle, e.g. an angle of rotation of a machine nacelle about a vertical axis, e.g. the tower axis and a pitch angle, e.g. a rotation of the rotor blades about their longitudinal axis, can be adjusted. 
     SUMMARY 
     In view of the above, a drive train supporting arrangement for a wind turbine including a drive train is provided, said drive train supporting arrangement including a hinge connection means adapted for pivotably supporting the drive train, a self-supporting structure adapted for supporting the hinge connection means, and a first lattice structure adapted for supporting a counterweight, the counterweight being connected to and acting on the drive train. 
     According to another aspect a wind turbine including a drive train and a drive train supporting arrangement is provided, said drive train supporting arrangement including a hinge connection means adapted for pivotably supporting the drive train, a self-supporting structure adapted for supporting the hinge connection means, and a first lattice structure adapted for supporting a counterweight-damper mass, the counterweight-damper mass being connected to and acting on the drive train. 
     According to yet another aspect a method for adjusting a tilt angle of a drive train of a wind turbine including a drive train and a drive train supporting arrangement is provided, said method including determining a wind shear at the location of the wind turbine, measuring an actual tilt angle of the drive train of the wind turbine, and changing the tilt angle of the drive train as a function of the actual tilt angle and the measured wind shear. 
     Further exemplary embodiments are according to the dependent claims, the description and the accompanying drawings. 
    
    
     
       DRAWINGS 
       A full and enabling disclosure, including the best mode thereof, to one of ordinary skill in the art is set forth more particularly in the remainder of the specification including reference to the accompanying drawings wherein: 
         FIG. 1  is a side view of a wind turbine having a tower and a machine nacelle arranged rotatably about a vertical axis, wherein the machine nacelle includes a vibration damper unit, according to a typical embodiment; 
         FIG. 2  is a top view of the wind turbine shown in  FIG. 1 , wherein an orientation of a rotor axis of the rotor is shown to be adjustable with respect to a yaw angle; 
         FIG. 3  is a side view of a drive train supporting arrangement, wherein the drive train includes a speed adapter unit and a generator, according to a typical embodiment; 
         FIG. 4  is a side view of a drive train supporting arrangement, wherein the drive train includes a speed adapter unit and a generator, according to another typical embodiment; 
         FIG. 5  is a side view of a drive train supporting arrangement, wherein the drive train includes a direct drive generator, according to yet another typical embodiment; 
         FIG. 6  is a side view of a drive train supporting arrangement, wherein the drive train includes a direct drive generator, according to yet another typical embodiment; and 
         FIG. 7  illustrates a flowchart explaining a method for adjusting a tilt angle of a rotor axis of a wind turbine in dependence of a measured wind shear. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the various exemplary embodiments, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations. 
     A number of embodiments will be explained below. In this case, identical structural features are identified by identical reference symbols in the drawings. The structures shown in the drawings are not depicted true to scale but rather serve only for the better understanding of the embodiments. 
       FIG. 1  illustrates a wind turbine  100  viewed from one side according to a typical embodiment. The wind turbine  100  includes a tower and a machine nacelle  103  arranged rotatably on the top of the tower  102 . The machine nacelle includes a rotor having at least one rotor blade  101 , a hub  104  and a main shaft  117 . Typically, the drive train of the wind turbine  100  includes the main shaft  117 , the rotor  104  and a gear box generator arrangement (described herein below). The machine nacelle  103  may be rotated about a vertical axis  107  such that the rotor blades and the main shaft  117  respectively can be oriented towards a wind direction  105  of the incoming wind. In dependence of the strength of the incoming wind, a bending moment  109  can occur at the entire wind turbine. The bending moment  109  acts about a typically horizontal axis being perpendicular to the vertical axis  107  and a rotor axis  115 . 
     In order to obtain a good energy conversion from wind energy into rotational energy, the at least one rotor blade  101  can be adjusted with respect to a pitch angle  108 . The pitch angle  108  is adjusted by rotating a respective rotor blade about its longitudinal axis. Thus, the pitch angle may determine loads as a function of the strength of the incoming wind  105  onto a specific rotor blade. 
     According to a typical embodiment, a vibration damper unit  114  is provided which is adapted to damp vibrations caused by varying wind forces and rotational influences. These vibrations (or oscillations) may act on the entire wind turbine  100 , e.g. several portions of the wind turbine are vibrating in a combined mode. Typically, these oscillations are dependent on the design of the wind turbine  100  and on meteorological conditions. 
     The vibration damper unit is arranged at a position where the oscillations may be effectively damped. Therefore, specific vibration frequencies of the mechanical arrangement of portions of the wind turbine  100  or of the entire wind turbine  100  can be damped. In order to be effective, such kind of load reduction system typically is installed atop the tower  102 , e.g. inside or outside the machine nacelle  103 . Thus, it is possible that the vibration damper unit rotates about the vertical axis  107  together with the drive train of the wind turbine  100 . A counterweight which may be formed as a counterweight-damper mass may be provided as a liquid tuned damper. In a typical embodiment the liquid tuned damper may include water. 
       FIG. 2  is a top view of the wind turbine  100  shown in  FIG. 1 . A rotor axis  115  is defined by the axis of the main shaft  117  ( FIG. 1 ) and can be directed towards the incoming wind direction  105  by changing the yaw angle  106 . When the rotor having the plurality of rotor blades  101  rotates, vibrations may occur which are damped by the an active or passive vibration damper unit  114 . If wind shear is present at the location of the wind turbine, e.g. if the wind velocity in lower regions near ground is less than the wind velocity in higher regions high above ground, according to a typical embodiment, the rotor axis  115  is not only adjusted with respect to the incoming wind direction  105  by changing the yaw angle  106 , but also with respect to an axis which is perpendicular to the vertical axis  107  ( FIG. 1 ) and the rotor axis  115 . This axis is called the tilt axis, and the angle of rotation about this tilt axis is the tilt angle  116  (see below  FIG. 3-6 ). 
     In order to rotate the drive train of the wind turbine  100  about the tilt axis  118  being perpendicular to the vertical axis  107  and the rotor axis  115 , a drive train supporting arrangement is provided according to typical embodiments shown in  FIG. 3-6 . 
       FIG. 3  illustrates a drive train supporting arrangement  200  according to a typical embodiment. A self-supporting structure  207  is arranged atop the tower  102 . The self-supporting structure  207  is mounted at a tower bearing  119  by means of mounting units  120 . A hinge connection means  201  is fixed to the self-supporting structure  207  at a front end thereof, e.g. at an end directed towards the hub  104  of the wind turbine  100 . The hinge connection means  201  may include a damping mechanism such as an oil damper unit. 
     In the typical embodiment shown in  FIG. 3 , the drive train of the wind turbine  100  includes the rotor having a plurality of rotor blades  101  and the rotor axis  115 , a speed adapter unit  113  and a generator  112 . The speed adapter unit  113  is used to adapt a rotational speed of the rotor to a required input rotational speed of the generator  112 . In a typical embodiment, the speed adapter unit may include a gear box. The drive train including the rotor, the speed adapter unit  113  and the generator  112  is adapted for a connection to the self-supporting structure  207  wherein the connection is rotatable about a typically horizontal axis. 
     Therefore, the hinge connection means  201  is adapted for pivotly supporting the drive train. A tilt angle detection unit  210  is provided in order to measure an actual tilt angle  116 , and/or a change of the tilt angle  116 . the tilt angle  116  is thus a measure of the orientation of the rotor axis  115 . The self-supporting structure may form a part of a machine nacelle  103  (shown in  FIGS. 1 and 2 ) and may include a closed housing by applying flexible bellows  209  which are connected to a tiltable part of the drive train. A counterforce is provided by a counterweight  203  which is connected to a first lattice structure  202 . The gravitational force  212  of the counterweight  203  is transferred to the tiltable drive train by means of a cable  204 . Moreover the counterweight may act as a damper mass for damping vibrations. Such kind of counterweight-damper mass may be movable with respect to the drive train in directions  208 , e.g. horizontally such that wind thrust at the rotor blades may be compensated. 
     As shown in  FIG. 3 , the first lattice structure  202  is also connected to the mounting units  120  which are used to connect the self-supporting structure  207  to the tower bearing  119 . By changing the weight value of the counterweight  203 , it is possible to change the force acting onto the cable  204  and thus to change the tilt angle  116  of the entire drive train. More conveniently, the counterweight  203  is moved in a direction shown by arrows  208  in order to adjust the tilt angle  116  of the rotor axis  115  and the drive train, respectively. The moment which acts onto the rotor axis  115  is determined by the weight of the counterweight  203  and the distance between the counterweight and the tower axis  107  ( FIG. 1 ). 
     At its top end, the first lattice structure  202  may include an anemometer support unit  205  for supporting an anemometer  206 . The anemometer support unit  205  is adapted for arranging the anemometer  206  distant from air turbulences caused by the rotating rotor blades. The anemometer  206  which is installed at this location distant from the main rotor having the plurality of rotor blades  101  is less influenced by wind deviations caused by the rotating rotor blades  101  and thus provides a better measurement accuracy as compared to anemometers which are installed closer to the tower axis (vertical axis)  107 . 
     It is noted here that besides adapting the tilt angle  116  of the rotor axis  115  with respect to a horizontal wind shear of the incoming wind  105 , the tilt angle  116  of the rotor axis  115  may be adapted according to loads measured at different locations within the wind turbine  100 . Furthermore, it is noted that the drive train supporting arrangement  200  having a self-supporting structure  207  and a first lattice structure  202  is a lightweight construction which saves yaw energy and eases installation of the wind turbine. The movement of the counterweight in the counterweight movement direction  208  may be used to counteract thrust changes caused by the incoming wind  105 . 
       FIG. 4  illustrates a drive train supporting arrangement for a drive train including the rotor, the speed adapter  113  and the generator  112 , according to another typical embodiment. 
     It is noted here that components or steps which have been described with respect to previous drawings, are not repeated in the following sections in order to avoid a redundant description. Furthermore, an explanation of reference numerals which have been explained in previous drawings in the description, are not extensively repeated in the description of succeeding drawings. 
     As in the typical embodiment shown in  FIG. 3 , a self-supporting structure  207  is provided which is connected to the tower bearing  119  of the tower  102  by means of at least two mounting units  120 . 
     Again, the self-supporting structure  207  is at a fixed position wherein in the embodiment shown in  FIG. 4  the hinge connection means  201  is supported by a second lattice structure  211  which is connected by second mounting units  121 . The drive train now is rotatable about the axis of the hinge connection means  201  which is connected to the drive train at the front end of the speed adapter  113 . As in the embodiment shown with respect to  FIG. 3 , a first lattice structure  202  is provided which is connected to the tower bearing  119  by means of the mounting units  120 . 
     The counterweight  203  now acts on three different portions of a cable  204 . The first portion of the cable  204  is connected to the drive train, wherein the second and third portions of the cable  204  are connected to the second lattice structure  211 . 
     As the first lattice structure  202 , the second lattice structure  211  is lightweight such that the entire drive train supporting arrangement  200  has a reduced weight as compared to a machine nacelle without any lattice structure. 
     A flexible bellow  209  is provided as a connection means between the drive train and the fixed self-supporting structure  207 . Again, the counterweight  203  may be moved in a direction of the arrows  208  such that the tilt angle  116  of the rotor axis  115  may be varied. 
     In the following, drive train supporting arrangements  200  according to further typical embodiments are explained with respect to  FIGS. 5 and 6 .  FIGS. 5 and 6  correspond to  FIGS. 3 and 4  with respect to the drive train supporting arrangement whereas the difference of  FIGS. 5 and 6  as compared to  FIGS. 3 and 4  is that the combination of the speed adapter  113  and the generator  112  ( FIGS. 3 and 4 ) has been replaced by a direct drive generator  111  ( FIGS. 5 and 6 ). 
     More precisely,  FIG. 5  corresponds to  FIG. 3  wherein the speed adapter  113  and the generator  112  have been replaced by the direct drive generator  111 .  FIG. 6  corresponds to  FIG. 4  wherein the speed adapter  113  and the generator  112  have been replaced by the direct drive generator  111 . Thus, the drive train supporting arrangement  200  of  FIG. 5  corresponds to the drive train supporting arrangement of  FIG. 3 , whereas the drive train supporting arrangement of  FIG. 6  corresponds to the drive train supporting arrangement  200  of  FIG. 4 . 
     As shown in  FIG. 5 , the hinge connection  201  is connected to the self-supporting structure  207  such that the direct drive generator  111  is tiltable about a horizontal axis (the tilt axis  118 ; see  FIG. 2 ) which is perpendicular to both the vertical axis  107  of the wind turbine ( FIG. 1 ) and the rotor axis  115 . A flexible bellow  209  is provided for connecting the direct drive generator  111  to the self-supporting structure  207 . At the upper end of the first lattice structure  202 , an anemometer support unit  205  with an anemometer  206  is provided, as explained with respect to  FIG. 3 . 
       FIG. 6  illustrates a drive train supporting arrangement  200  according to yet another typical embodiment. In addition to the first lattice structure  202 , a second lattice structure  211  is provided which is connected to the self-supporting structure  207  at the location of the hinge connection means  201 . A tilt angle detection unit  210  detects the tilt angle  116  of the drive train including the rotor having a plurality of rotor blades  101  and the hub  104  and the direct drive generator  111  about the tilt axis  118  ( FIG. 2 ). 
     As in the embodiment shown with respect to  FIG. 4 , three portions of a cable  204  are provided. A first portion of the cable  204  transfers the gravitational force  212  of the counterweight  203  to the drive train, wherein the second and third portions of the cable  204  hold the second lattice structure  211 . 
       FIG. 7  is a flowchart illustrating a method for adjusting a tilt angle of a drive train of a wind turbine  100  according to a typical embodiment. At step S 1 , the procedure is started. 
     At step S 2 , the wind at different heights of the wind turbine  100  is measured. Furthermore, a calculation and/or estimation of wind shear, e.g. from bending moments at the rotor blades, is carried out. Such kind of wind measurement results in a wind shear determination which may be used for appropriate adjustment of the rotor axis  115 . The procedure advances to step S 3  where the actual tilt angle  116  of the rotor axis  115  is measured. If the actual tilt angle  116  is adapted to the measured wind shear (“Yes” at step S 4 ), the procedure proceeds to step S 6 . 
     It is noted here that wind shear can be measured using anemometers at different hub heights. Moreover wind shear can be calculated from measurements of loads or deflections of at least one rotor blade. 
     When it is determined at step S 4  that the actual tilt angle  116  is not adapted for the measured wind shear (“No” at step S 4 ), then the procedure advances to step S 5  where the tilt angle is changed according to the measured wind shear. The tilt angle may be changed by moving the counterweight  203  in the counterweight moving direction  208  (see  FIG. 3-6 ). 
     Then the procedure advances to step S 6  where it is determined whether the wind shear has changed or not. The determination of any change of wind shear again may be performed by wind velocity sensors installed at different heights at the wind turbine  100 . If the wind shear has changed (“Yes” at step S 6 ), the procedure returns to step S 2 , and the procedural steps S 2  to S 5  (S 4 ) are repeated. If it is determined that the wind shear did not change (“No” at step S 6 ), the procedure is ended at step S 7 . 
     The invention has been described on the basis of embodiments which are shown in the appended drawings and from which further advantages and modifications emerge. However, the disclosure is not restricted to the embodiments described in concrete terms, but rather can be modified and varied in a suitable manner. It lies within the scope to combine individual features and combinations of features of one embodiment with features and combinations of features of another embodiment in a suitable manner in order to arrive at further embodiments. 
     It will be apparent to those skilled in the art, based upon the teachings herein, that changes and modifications may be made without departing from the disclosure and its broader aspects. That is, all examples set forth herein above are intended to be exemplary and non-limiting.