Abstract:
A vibration-resistant wind turbine and process for operation is provided. The wind turbine has a rotor with at least two blades, each of which includes an inclinometer arrangement with at least two axes, and an evaluating unit. The evaluating unit determines the bending and/or twisting of the blade relative to the longitudinal axis of the blade on the basis of signals from the inclinometer arrangement for each blade during operation. Each rotor blade further has at least one liquid tank which is capable of receiving or transferring liquid from or to a liquid reservoir via a transfer mechanism in response to the determined bending and/or twisting of the rotor blades to reduce vibration caused by imbalances, thereby extending the service life of the wind turbine.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to a vibration-resistant wind turbine, and is specifically concerned with a wind turbine having a rotor with at least two blades, each of which includes an inclinometer arrangement with at least two axes, and a process of operation. 
     2. Description of Related Art 
     Wind turbines typically comprise a rotor—with a hub and three rotor blades—that is mounted in horizontal orientation in an engine housing. The housing accommodates a rotor-driven generator and is mounted to rotate on a tower. In general, the rotor blades are mounted in an adjustable manner on the rotor hub to control the angle of attack of each individual rotor blade separately. In current research, it is even considered to also adjust parts of the rotor blade separately. By such an adjustment of the angle of attack (also referred to as pitch angle), the speed of the rotor can be regulated. 
     Wind turbines are basically subject to vibration, in particular because of the rotor being out of balance. The imbalances that occur are due primarily to either mass imbalances or aerodynamic imbalances. Mass imbalances may arise because of unequal rotor blade masses or unequal mass distributions in the individual rotor blade, hub imbalances, eccentricities of the complete rotor, icing on the rotor blades, or water penetration inside the rotor blades. Aerodynamic imbalances may arise because of blade angle errors, unequal rotor blade profile shapes, rotor blade damage, oblique inflow of the rotor, as well as site-based excitations from outside, (e.g., by tower resonance and the fact that the wind speed generally depends on the height above ground such that one and the same rotor blade is exposed to different aerodynamic forces, depending on whether it is just below or above). Such imbalances result in a reduced service life of the wind turbine. Minimization of the imbalances of the rotor is therefore desirable. Also, a diagnosis of the operating state of the wind turbine is advantageous in order to shut down the wind turbine for safety reasons when unacceptable stresses occur or to determine defective components and to exchange them in a timely fashion. 
     A survey on the vibration problem in wind turbines can be found in, for example, the magazine telediagnose.com, Edition No. 12. 
     Described in German Patent Application DE 102 19 664 A1 and corresponding U.S. Pat. No. 6,940,186 is a wind turbine in which sensor elements are provided for determining mechanical stresses of the rotor on the rotor blades and on the rotor shaft in order to adjust the rotor blades based on the mechanical stresses that are determined. The sensors that are provided on the rotor shaft are used to detect pitch and yaw moments. Also, the rotor blades can be provided with ballast tanks in order to pump water from a storage tank provided in the hub into the ballast tanks or to drain water from the ballast tanks into the storage tank in order to minimize possible rotor imbalance by trimming. While the filling of the ballast tanks is possible even during operation, the rotor in the corresponding position has to be shut down when draining a ballast tank. 
     From German Patent Application DE 10 2004 014 992 A1, a wind turbine is known in which an imbalance sensor is provided to determine the imbalance of the rotor, and the rotor blades are provided with balance weights that can be adjusted in axial direction and that can be adjusted corresponding to the determined imbalance in order to minimize the imbalance of the rotor. 
     In general, European Patent Application EP 1 674 724 A2 and corresponding U.S. Publication No. 2006/0140761 describes the monitoring of components of a wind turbine by means of various sensors, for example acceleration sensors, gyroscopes, proximity sensors, and inclinometers, and, in reference to the monitoring of rotor blades, the use of proximity sensors—by means of which the bending of the blades is to be detected—is described. 
     International Patent Application Publication WO 01/33075 A1 and corresponding U.S. Pat. No. 6,619,918 describes the load-sensing equipment of strain gauges attached to the rotor blades of a wind turbine for the purpose of controlling the pitch adjustment of the blades. 
     International Patent Application Publication WO 2006/012827 A1 and corresponding U.S. Publication No. 2008/0206052 describes the monitoring of the state of the rotor blades of a wind turbine during operation by means of solid-borne sound conduction, whereby movement sensors are arranged on the blades. 
     International Patent Application Publication WO 2006/039903 A1 and corresponding U.S. Patent Publication No. 2008/0067814 describes a pitch adjustment of the rotor blades of a wind turbine implemented by monitoring the pressure difference between the front side of the blade and the back side of the blade. 
     International Patent Application Publication WO 2007/131489 A1 and corresponding U.S. Publication No. 2009/031199 describes the use of acceleration sensors on the rotor blades of a wind turbine for the purpose of regulating the pitch angle, whereby vibration measurements are made. 
     International Patent Application Publication WO 2008/058876 A2 describes that for the purpose of preventing rotor blades from colliding with the tower of a wind turbine, distance sensors can be arranged on the tower or on the housing in order to measure the distance from the respective rotor blade to a prescribed location of the wind turbine and optionally to emit a collision warning. 
     International Patent Application Publication WO 2005/068834 A1 and corresponding U.S. Publication No. 2007/0297892 relates to a wind turbine in which the state of the rotor blade is monitored by means of strain gauges, and the position of the rotor blade is monitored by means of GPS. 
     The monitoring of the state of the rotor blades by means of strain gauges is problematic in as much as strain gauges are difficult to install and are relatively short-lived. Furthermore, strain gauges measure, in principle, only locally in the structure of the rotor blade. This shortcoming also applies to acceleration sensors or movement sensors. 
     SUMMARY OF THE INVENTION 
     A primary object of this invention is to implement a state-monitoring of the rotor blades of a wind turbine as reliably as possible. 
     This object is achieved by providing each rotor blade of a wind turbine with at least one inclinometer arrangement that has at least two axes, in combination with an evaluating unit in communication with the at least one inclinometer arrangement. The evaluation unit determines the bending and/or twisting of the blade relative to the longitudinal axis of the blade, thus making possible a reliable evaluation of the state relative to the operationally induced deformations of the rotor blades. It is especially advantageous that by means of inclinometers, reference to the direction of rotation or to the geocenter is produced, i.e., an absolute frame of reference is predetermined by which the accuracy of the measurement of the deformation of the rotor blade can be achieved. Furthermore, the pitch adjustment of the rotor blades can also be monitored by means of the inclinometer arrangement. 
     The invention further includes a process for operating a wind turbine with a rotor with at least two blades that in each case are provided with at least one inclinometer arrangement with at least two axes. In this process, a when a change in the inclination of the inclinometer arrangement is detected for a blade, the bending and/or the twisting of the blade relative to the longitudinal axis of the blade is determined. 
     Below, the invention is explained in more detail by way of example with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic example of a wind turbine according to the invention; and 
         FIG. 2  is a block diagram of the essential components of the wind turbine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a diagrammatic example of a wind turbine according to the invention. In this case, a rotor  10  is provided with a hub  12  for three rotor blades (of which only two rotor blades  14 A,  14 B are shown in  FIG. 1 ). The rotor  10  is mounted in horizontal orientation in a nacelle  16 , which accommodates a generator  18  that is driven by the rotor shaft  20  via a drive  22 . The nacelle  16  is mounted on a tower  24  to rotate around a vertical axis. The housing also has a sensor  26  for the wind speed and the wind direction. In addition, a sensor  28  is provided for the detection of the speed of the rotor  10 . 
     In each rotor blade  14 A,  14 B, at least one inclinometer arrangement that has at least two axes is provided (in the example, two inclinometer arrangements  30 A,  31 A or  30 B,  31 B that are offset on each rotor blade in the longitudinal direction of the blade are shown). The inclinometer arrangements are provided in order to determine the bending and/or twisting of the blade relative to the longitudinal axis of the blade for each rotor blade during operation. The bending of the rotor blade relative to the longitudinal axis of the blade can be determined when the inclinometer arrangement is arranged such that it can detect a change in the inclination of the inclinometer arrangement relative to a plane that is perpendicular to the longitudinal axis of the blade (in the case of a two-axis inclinometer, this corresponds to the plane that is formed by the two-axis inclinometer). Twisting of the rotor blade relative to the longitudinal axis of the blade can be detected when the inclinometer arrangement is arranged such that it can detect a movement of the inclinometer around the longitudinal axis of the rotor blade (in this case, the corresponding axis of the inclinometer has to be parallel to the longitudinal axis of the rotor blade). 
     The rotor blades  14 A,  14 B can be adjusted in each case by means of a pitch controller  32  around their longitudinal axis relative to the hub  12  in order to implement a pitch adjustment of the rotor blades  14 A,  14 B in the usual way. In this case, preferably each rotor blade  14 A,  14 B is adjusted individually. 
     In each rotor blade  14 A,  14 B, at least one liquid tank  34  is provided that is connected via lines  36  to a distributor arrangement  38 . The distributor arrangement  38  is connected to a pump  40  that in turn is connected to a liquid reservoir  42 . The distributor arrangement  38 , the pump  40 , and the liquid reservoir  42  are arranged in a fixed manner in the hub  12  relative to the hub  12  and rotate correspondingly when the rotor  10  is in operation. Also, a unit  44  is provided in order to control the pump  40  or the distributor arrangement  38 . The liquid can be, for example, water, optionally with the addition of antifreeze, e.g., glycol. 
     The signals from the speed sensor  28 , the wind gauge  26 , and the inclinometer arrangements  30 A,  31 A,  30 B,  31 B are directed into the data-processing unit  44 . In the data-processing unit  44 , the bending and/or rotation of the blade relative to the longitudinal axis of the blade is determined from the signals from the inclinometer arrangements for each blade, from which then conclusions are drawn on a mass imbalance and an aerodynamic imbalance of the respective rotor blade. On the one hand, the signals from the inclinometer arrangements that are processed or evaluated in this way can be used as criteria for a rapid shut-down of the wind turbine when preset boundary values are exceeded. The evaluation of the signals from the inclinometer arrangements can be implemented by means of time range averaging, frequency analysis, classification, and/or event monitoring, whereby the classification can be implemented by means of a rainflow-counting algorithm. 
     The evaluated data or else the signals from the inclinometer arrangements in the original form or in a pre-processed intermediate form can be forwarded online via a data transfer device  48  to a diagnostic site  50  that is arranged removed from the wind turbine  10  in order to evaluate the state of the wind turbine. In this case, the data transfer preferably is implemented by Internet and can be actively requested, for example, by the diagnostic site  50  or automatically implemented at certain intervals by e-mail. The diagnostic site  50  comprises a data-processing unit  52  for processing the received data as well as a display device  54  for displaying the processed data. 
     The unit  44  also preferably has an input for the pitch controller  32  and an input for the wind sensor  26 . From the rotor imbalance or blade deformations determined by means of the signals from the inclinometer arrangements, optionally taking into consideration the pitch controller  32  and the signals from the wind sensor  26 , the control device  44  produces a control signal for the liquid transfer mechanism formed by the pump  40  and the distributor  38  in order to selectively transfer liquid between the liquid reservoir  42  and the liquid tank  34  based on the imbalance that is detected in order to continuously minimize the imbalance of the rotor  10 . 
     As input signals, the pitch controller  32  takes into consideration, i.a., the signals from the wind sensor  26  and the speed sensor  28  as well as an output signal from the control unit  44 , this being representative of the detected rotor imbalance or deformation of the respective blade. In this way, the pitch controller  32  uses the speed regulation and can in addition assist in the compensation of imbalances of the rotor  10 . In this case, a smoothing of the dynamics of the pitch is made possible by the described recycling of liquid into or from the tanks  34 . 
     The power supply of the rotating pump  40  is implemented preferably via a slip ring (not shown). 
     In the configuration of the tank  34  that is shown in  FIG. 1 , the supply/discharge lines  36  are connected respectively to the end of the tank  34  that is far from the rotor hub  12 , by which in the rotating rotor  10 , not only the possibility of the liquid supply to the tanks  34 , but also the possibility of the liquid discharge from the tanks  34  is ensured at all times since because of the centrifugal force, liquid is always available at the end of the tank  34  that is far from the rotor hub  12 , even if the tank  34  contains only a little liquid and if there is air in the system. In principle, in such a configuration of the tank  34 , it can be designed with rigid walls or like a bag with flexible walls. 
     In principle, a single tank  34  or else several such tanks can be provided per rotor blade  14 A,  14 B. Also, instead of a single storage reservoir  42 , a multiple of such reservoirs can be provided. Also, instead of a pump  40  that is provided in common for all tanks  34 , for example for each of the rotor blades  14 A,  14 B or for each of the tanks  34 , a separate liquid pump can be provided. Instead of as a block as shown in  FIG. 1 , the distributor arrangement  38  can be implemented, i.e., as a three-way valve, even by separately controlled valves in each of the supply/discharge lines  36 . 
     The signals from the inclinometer arrangements can also be used in order to monitor the pitch controller  32 . Conversely, as already mentioned, the signals from the inclinometer arrangements can be taken into consideration in the control of the pitch controller  32 . 
     In the main bearing of the hub (not shown), an imbalance sensor can also be provided in the form of a vibration sensor  56  in order to detect an imbalance of the rotor  10  during operation. The signals from the imbalance sensor  56  are also fed into the data processing unit  44  and can be taken into consideration in the diagnosis of the wind turbine as well as in the control of the pitch  32  or the control of the liquid pump  40 .