A method and a system for tracking motion of a blade

Abstract

The present invention relates to a method and a system for tracking the motion of a blade of a wind turbine. One embodiment relates to a blade motion tracking system for installation on a wind turbine blade, where the wind turbine blade comprises a blade root and a blade tip. The system comprises at least one light module comprising at least a first light source, preferably adapted to emit light in the direction of the blade root. An optical measuring device is provided, preferably located at the blade root, adapted to receive light emitted from the first light source(s). The optical measuring device is preferably a position sensitive detector identifying the position of the first light source relative to the position sensitive detector. A single light source located at the tip of the blade, close to the tip of the or towards the tip of the blade, is sufficient to measure deflection of the blade. Advantageously the first light source is modulated with a predefined modulation frequency such that light from the first light source can be distinguished from ambient light and thereby minimize the influence of the ambient light conditions during detection.

1 . A blade motion tracking system for installation on a wind turbine blade, where the wind turbine blade comprises a blade root and a blade tip, and a leading edge and a trailing edge with a chord length extending therebetween of each blade section; said system comprising
 at least one light module comprising a first light source in a blade section at a predetermined distance from the blade root, said first light source configured for having a predefined modulation frequency, and   an optical measuring device adapted to receive light emitted from the first light source, and wherein the optical measuring device comprises at least one position sensitive detector (PSD) for identifying the position of the first light source relative to the position sensitive detector, and wherein the optical measuring device is configured for distinguishing the first light source from ambient light conditions based on the predefined modulation frequency.   
     
     
         2 . The system according to  claim 1 , wherein the light module is provided near the tip of the blade. 
     
     
         3 . The system according to  claim 1 , wherein the optical measuring device, or at least a PSD thereof, is provided at the blade root. 
     
     
         4 . The system according to  claim 1 , wherein the PSD is a one-dimensional PSD. 
     
     
         5 . The system according to  claim 1 , wherein the PSD is at least a two-dimensional PSD. 
     
     
         6 . The system according to  claim 1 , wherein the PSD is a non-discrete PSD. 
     
     
         7 . The system according to  claim 1 , wherein the light module comprises at least a second light source, adapted to emit light in the direction of the blade root, the first and second light sources provided on or near the leading edge and the trailing edge respectively in a blade section at a predetermined distance from the blade root, and wherein the optical measuring device is configured for receiving light emitted from the light sources, and wherein the PSD is at least a two-dimensional PSD configured for identifying the position of each of the first and second light sources relative to the PSD. 
     
     
         8 . The system according to  claim 7 , wherein the second light source is modulated with a predefined modulation frequency, which is different from the modulation frequency of the first light source, and wherein the optical measuring device is configured for distinguishing the first light and second light sources 1) from each other based on the different modulation frequencies, and 2) from ambient light conditions based on the predefined modulation frequencies. 
     
     
         9 . The system according to  claim 1 , wherein the position sensitive detector is provided with a lens and an optical filter adapted to receive the light from the light source(s)s through said lens and said filter. 
     
     
         10 . The system according to  claim 1 , wherein the position sensitive detector further comprises a signal processing system for demodulating an output signal from the PSD to identify the relative position of the first light source and optionally the second light source. 
     
     
         11 . The system according to  claim 1 , wherein one or more further light modules are provided in one or more blade sections between the root and the tip region, and wherein the optical measuring device is capable of identifying each of the light sources in the multiple light modules. 
     
     
         12 . The system according to  claim 7 , wherein a multiple of modulation frequencies are used for the light sources. 
     
     
         13 . The system according to  claim 1 , wherein the light source(s) is an LED. 
     
     
         14 . The system according to  claim 1 , wherein the light source(s) is a laser. 
     
     
         15 . (canceled) 
     
     
         16 . A method for tracking the motion of a blade of a wind turbine, where the wind turbine blade comprises a blade root and a blade tip, and a leading edge and a trailing edge with a blade section extending therebetween of each blade section; the method comprising the steps of:
 providing at least a first light module comprising at least a first light source modulated with a predefined modulation frequency;   providing a position sensitive detector (PSD), preferably at the blade root, adapted to receive light emitted from the first light source of said first light module, and   distinguishing the first light source from ambient light by means of the predefined modulation frequency, and identifying the relative position of first light source, by means of the position sensitive detector.   
     
     
         17 . The method according to  claim 16  wherein the at least first light module further comprises at least a second light source, and wherein the first and second light sources are provided on the leading edge and the trailing edge, respectively, in a predetermined blade section, preferably near the blade tip, said first and second light sources being frequency modulated with different predefined modulation frequencies,
 providing an optical measuring device, preferably at the blade root, adapted to receive the light emitted from the light sources of said first light module, and 
 distinguishing each light source based on the different modulation frequencies and identifying the relative position of each of the light sources in the position sensitive detector. 
 
     
     
         18 . The method according to  claim 16 , wherein the light module is provided near or on the tip of the blade. 
     
     
         19 . The method according to  claim 16 , wherein the optical measuring device, or at least a PSD thereof, is provided at the blade root. 
     
     
         20 . The method according to  claim 16 , wherein the PSD is a one-dimensional PSD. 
     
     
         21 . The method according to  claim 16 , wherein the PSD is a non-discrete PSD. 
     
     
         22 . The method according to  claim 16 , whereby the method is performed with a data rate allowing for real-time tracking of the blade motion. 
     
     
         23 . The method according to  claim 16 , whereby the tracking of the blade motion includes a plurality of light modules with light sources on the leading edge and trailing edge of a multiple of blade sections. 
     
     
         24 . The method according to  claim 16 , whereby the light sources are synchronised. 
     
     
         25 . (canceled) 
     
     
         26 . The method according to  claim 16 , whereby the light source(s) is/are provided on a rear side of the wind turbine blades. 
     
     
         27 . A method of controlling a wind turbine having a rotor with a plurality of wind turbine blades, the wind turbine having a blade motion tracking system comprising:
 at least one light module comprising a first light source in a blade section at a predetermined distance from a blade root, said first light source configured for having a predefined modulation frequency, and   an optical measuring device adapted to receive light emitted from the first light source, and wherein the optical measuring device comprises at least one position sensitive detector (PSD) for identifying the position of the first light source relative to the position sensitive detector, and wherein the optical measuring device is configured for distinguishing the first light source from ambient light conditions based on the predefined modulation frequency;   wherein at least a wind turbine blade pitch and a yaw of the rotor are controlled using measurements of blade tracking by performing a method according to  claim 16 .