WIND BLADE AND METHOD OF OPERATING A WIND TURBINE BLADE

BACKGROUND

[1] The invention relates generally to wind turbines and more particularly to a wind blade and a method of operating a wind turbine blade.

[2] A conventional wind turbine includes a rotor with one or more wind blades and a hub. The wind blades convert wind energy into a rotational torque that is used to a generator that is rotationally coupled to the rotor through a drive train. The boundary layer of an air flow at a surface of the wind blade and the distribution of the air flow around the surface of the wind blade are factors that affect the energy conversion efficiency of the wind turbine. With the passage of time, the surface texture of wind blades becomes altered due to accumulation and deposition of airborne particles such as dust, pollen, insects, and sand. These depositions increase surface roughness of the wind blade and change the aerodynamics of the air flow, in some cases by creating turbulent flow throughout the entire chord of the airfoil starting from a leading edge. Aerodynamics properties, such as design angle of attack, maximum lift to drag ratio, design coefficient of lift (CL), stall margin, and slope of CL-alpha curve, are different under turbulent flow conditions as compared to clean flow or laminar or transitional flow conditions. When the wind blade experiences fully turbulent flow, the optimal settings for maximum energy extraction of operational parameters such as TSR (Tip Speed Ratio), revolution per minute (RPM), and pitch angle are different from such settings under clean flow or laminar or transitional flow conditions.

[3] Accordingly, it would be desirable to sense the surface roughness of rotor wind blade and efficiently operate the wind turbine for maximum energy extraction.

BRIEF DESCRIPTION

[4] In accordance with an embodiment of the invention, a wind blade is provided. The wind blade includes an aerodynamic blade body having a leading edge and a trailing edge. The wind blade also includes a sensing device coupled to the leading edge for sensing changes in the surface roughness of the leading edge.

[5] In accordance with an embodiment of the invention, a wind blade is provided. The wind blade includes a photovoltaic layer comprising a plurality of thin photovoltaic cells deposited on a flexible substrate attached to a leading edge of the wind blade. Further, the photovoltaic layer also includes a transparent conducting coating for sensing light and generating a corresponding current value.

[6] In accordance with an embodiment of the invention, a method of operating a wind turbine is provided. The method includes sensing surface roughness on a leading edge of the wind blade by using a sensing device attached to the wind blade. The method also includes controlling at least one operational parameter of the wind blade based on the sensed surface roughness of the wind blade to increase operating efficiency of the wind turbine.

DRAWINGS

[7] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[8] FIG. 1 is perspective view of a wind blade in accordance with an embodiment of the present invention.

[9] FIG. 2 illustrates a thin film anemometer with a feedback circuit for sensing surface roughness of a wind blade in accordance with another embodiment of the present invention.

[10] FIG. 3 illustrates a thin film photovoltaic sensing device of a wind blade in accordance with another embodiment of the present invention.

[11] FIG. 4 illustrates a structure of a photovoltaic cell of a thin film photovoltaic sensor of a wind blade in accordance with an embodiment of the present invention.

[12] FIG. 5 illustrates a wind blade with an optical sensor in accordance with another embodiment of the present invention.

[13] FIG. 6 illustrates a wind blade with a thin film strain gauge sensor n accordance with another embodiment of the present invention.

[14] FIG. 7 is a flow chart for a method of operating a wind turbine in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[15] When introducing elements of various embodiments of the present invention, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters are not exclusive of other parameters of the disclosed embodiments.

[16] FIG. 1 illustrates a wind blade 10 of a wind turbine in accordance with an embodiment of the present invention. The wind blade 10 includes an aerodynamic blade body having a leading edge 12 and a trailing edge 14. The wind blade 10 includes a sensor assembly 15 having a sensing device 16 coupled to the leading edge 12 for sensing changes in the surface roughness of the leading 12 edge. Often a cause of such surface changes is deposition of airborne particles such as dust, pollen, insects, and sand. The sensing device 16 may be deposited on a flexible substrate, wherein the flexible substrate is glued proximate to a root 18 of the blade body. In a non-limiting example, the flexible substrate along with the sensing device 16 is glued anywhere between the root 18 and about one-fifth length of the wind blade 10 from a center of the wind blade rotor hub. In one embodiment, the sensing assembly 15 includes one or more lead coupling the sensing device 16 to a control unit or processor located remotely or within a turbine hub (not shown) for processing of sensed information. The control unit may process the sensed information to determine a level of surface roughness on the leading edge 12 and accordingly determine the wind turbine setting for at least one corresponding operational parameter at that level of surface roughness for maximum energy extraction. Non-limiting examples of the operational parameters include tip speed ratio (TSR) and pitch angle of the wind blade 10.

[17] In one embodiment, the sensor assembly 15 of FIG. 1 comprises an anemometer with a probe located on the leading edge 12 for sensing changes in flow over the blade body with the passage of time and thus determining surface roughness. FIG. 2 illustrates a thin film anemometer 20. In a non-limiting example, the 'thin film' may refer to a thickness range from about 1 millimeter to about 5 millimeter. The thin film ensures that there is no significant change in boundary layer flow of the leading edge 12 of the blade body due to the presence of sensor assembly 15. In one embodiment, the blade body may have an indentation to accommodate the thin film anemometer 20 and maintain a smooth surface of the blade body without any protrusion of the thin film anemometer. The thin film anemometer 20 may be used to provide data representative of a heat transfer rate from a heated component 22 that is dependent upon various flow rate conditions over the heated component. The heated component 22 may comprise a thermally conductive hot plate, film, or wire coupled to the surface of the leading edge 12 of the wind blade 10 of FIG. 1. In one embodiment, the heated component comprises a thin film component coupled to the wind blade via a flexible substrate (not shown in FIG. 2). To maintain the heated component 22 at a constant temperature, a feedback circuit 24 may be used. In a more specific embodiment, the heated component 22 forms part of a Wheatstone bridge 26, such that resistance of the heated surface or probe 22 is kept constant over a bandwidth of the feedback circuit 24. Since the voltage of the heated component 22 is a simple potential division of an output voltage, the output voltage may be measured for convenience. The heat transfer rate from the heated component 22 is several orders of magnitude higher for the turbulent flow due to increased surface roughness as compared to the laminar flow. Hence when the flow is turbulent, the voltage required to maintain the heated surface or probe 22 at a constant temperature is significantly higher than the voltage required for the laminar flow. This voltage may be measured to determine surface roughness. In another related embodiment, the feedback circuit 24 may further includes a servo amplifier 28 and a bridge voltage meter 30 for controlling the voltages by varying current. During increased surface roughness of the leading edge 12, because the heat removal rate from the probe of the thin film anemometer is higher, there is a requirement of higher current to maintain constant temperature at the probe as compared to a clean flow or laminar flow. Thus, the differences in requirements of current may be used to determine surface roughness of the leading edge 12 of the wind blade 10 of FIG. 1 by the thin anemometer 20 of FIG. 2.

[18] In yet another embodiment, the sensing device 16 of FIG. 1 comprises a thin film photovoltaic sensing device 42 as shown in a wind blade 40 of FIG. 3. The thin film photovoltaic sensing device 42 comprises one or more photovoltaic cells 50. The thin film photovoltaic sensing device may be glued to the leading edge 12 of the wind blade 10 (as shown in FIG. 1).

[19] FIG. 4 illustrates a structure of a photovoltaic cell 50 as shown in FIG. 3 of a thin film photovoltaic sensing device of a wind blade in accordance with an embodiment of the present invention. In one embodiment, the photovoltaic cells 50 comprise polycrystalline thin-film cells made of small crystalline grains of semiconductor materials. In one embodiment, each photovoltaic cell 50 comprises a transparent conducting coating 52 and an antireflection coating 54 adjacent to the transparent conducting coating. The photovoltaic cell 50 in the example of FIG. 4 further includes a top n-type window layer 56 adjacent to the antireflection coating and a bottom p-type absorber layer 58 adjacent to the top n-type window layer 56. In a more specific embodiment, wherein the top n-type window layer 56 is formed by a first semiconductor material and the bottom p-type absorber layer 58 is formed by a second, different semiconductor material. In a non-limiting example, the first semiconductor material of the top n-type window layer 56 comprises cadmium sulfide (CdS), and the second semiconductor material of the bottom p-type absorber layer 58 comprises zinc telluride. The photovoltaic cell 50 further includes an ohmic contact layer 60 provided between the bottom p-type absorber layer 58 and a flexible substrate 62. FIG. 4 additionally illustrates a junction 64 formed between the top n-type window layer 56 and the bottom p-type absorber layer 58.

[20] If desired, the thin film photovoltaic sensing device may comprise multiple photovoltaic strips each with multiple photovoltaic cells 50. The multiple photovoltaic strips are in turn attached to the leading edge of the blade. When the blade body and the photovoltaic strips are new, there is no deposition and all of the surface area of the photovoltaic cells is exposed to sunlight, thereby producing more current. As the wind turbine ages, depositions accumulate on the surface of the wind blade and also on the photovoltaic strips. When a reduced area on the photovoltaic strips receives light, the current produced drops. When the strip is fully contaminated, no electricity is generated. Thus, photovoltaic strips may be used as a deposition sensor wherein a level of deposition is correlated to the electricity generated by the photovoltaic cells and measured by a processor. Thus, in one embodiment, the processor senses surface roughness of the leading edge of the wind blade by comparing a first current value generated by the photovoltaic strip with multiple photovoltaic cells having no deposition of airborne particles to a second current value generated by the photovoltaic layer with deposition of airborne particles. For most accurate correlation, it is useful to be aware of the sunlight conditions when making the measurements so that increased cloud conditions do not result in false readings of increased surface roughness, for example.

[21] FIG. 5 illustrates a wind blade 60 with an optical sensor 62 in accordance with another embodiment of the present invention. The optical sensor 62 includes a camera 64 that is located in a transparent housing unit 66. As shown, in one embodiment, the transparent housing unit 66 may be shaped for easy retrofit at a leading edge 67 of the wind blade 60. The camera 64 is configured to take periodic images of the surface of the transparent housing unit 66 which may be used to determine contamination of the wind blade 60 and thereby the surface roughness of the leading edge 67. Prior to installation of the optical sensor 62 on the leading edge, the wind blade 60 or another representative wind blade may be may be calibrated to obtain information regarding contamination patterns due to deposition of airborne particles with respect to contamination of a location of the optical sensor 62. This calibration is used by a control unit or the processor to determine surface roughness of the leading edge 67 based on images obtained during operation of the wind blade. The control unit or processor may also generate a schedule maintenance alert based on the determined surface roughness of the blade body 60.

[22] In one embodiment, the sensing device 16 of FIG. 1 comprises one or more thin film strain gauge sensors 72 in a wind blade 70 with a leading edge 12 and a trailing edge 14 as shown in FIG. 6. The wind blade 70 shows an aerodynamic shape profile with a suction surface 74 and a pressure surface 76 on either side of the blade cord 78. The one or more thin film strain gauge sensors 72 measures shear stress on the surface of the leading edge 12. A velocity gradient for a laminar boundary layer flow is less compared to a turbulent boundary layer flow. Therefore, the shear stress on the blade will be lower for a laminar boundary layer flow than a turbulent boundary layer flow. This difference in the wall shear stress near the leading edge, of the wind blade may be used for sensing transition from laminar to turbulent flow and hence the increased surface roughness of the wind blade 10 of FIG. 1.

[23] FIG. 7 is a flow chart for a method 100 of operating a wind turbine in accordance with an embodiment of the present invention. At step 102, the method includes sensing surface roughness on a leading edge of the wind blade by using a sensing device attached to the wind blade. In one embodiment, the sensing device includes a thin film anemometer. In another embodiment, the sensing device includes a thin film strain gauge. In yet another embodiment, the sensing device includes a thin film photovoltaic sensor. In still another embodiment, the sensing device includes an optical sensor for measuring a turbulent flow over the wind blade. Also, the method further includes processing data sensed by the sensing device to determine a contamination level and determining recommended settings of operational parameters based on the contamination level. At step 102, the method includes controlling at least one operational parameter of the wind blade based on the sensed surface roughness of the wind blade to increase operating efficiency of the wind turbine. In one embodiment, the operational parameters include a tip speed ratio and a pitch angle of the wind blade. The method may further include using pre-installation calibration data representative of a contamination pattern of the wind blade due to deposition of airborne particles with respect to contamination of a location of the sensing device prior. In one embodiment, the method also includes generating alerts for scheduling maintenance of the wind turbine based on the sensed surface roughness of the blade body.

[24] Advantageously, embodiments of the present invention may be used to increase energy output of the wind turbine by adjusting wind turbine parameter setting in response to changing levels of surface roughness of the wind blade. ,

[25] Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional assemblies and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the assemblies and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[26] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

CLAIMS:

1. A wind blade comprising:

an aerodynamic blade body having a leading edge and a trailing edge;

a sensing device coupled to the leading edge for sensing changes in the surface roughness of the leading edge.

2. The wind blade of claim 1, wherein the sensing device comprises a thin film anemometer for sensing changes in turbulent flow over the blade body during increased surface roughness of the blade body.

3. The wind blade of claim 2, wherein the thin film anemometer comprises a heating component and an anemometer circuit for maintaining a constant temperature of the heating component.

4. The wind blade of claim 3, wherein the heating component and the anemometer circuit comprise a Wheatstone bridge and a feedback circuit for maintaining the the heating compoennt at the constant temperature by varying a current as needed to maintain the constant temperature.

5. The wind blade of claim 1, wherein the sensing device comprises a thin film strain gauge for measuring a shear stress on a surface of the leading edge of the aerodynamic blade body.

6. The wind blade of claim 1, wherein the sensing device comprises a thin film photovoltaic sensor attached to the leading edge of the blade body.

7. The wind blade of claim 1, wherein the sensing device is situated on a flexible substrate coupled to the leading edge proximate to a root of the blade body.

8. The wind blade of claim 1, wherein the sensing device comprises an a camera situated within the blade and facing a transparent window on the blade body for taking periodic images of the surface of the transparent window.

9. A sensing device for a wind blade, comprising:

a photovoltaic layer comprising a plurality of thin photovoltaic cells situated on a flexible substrate attached to a leading edge of the wind blade.

10. The sensing device of claim 9, wherein each of the photovoltaic cells comprises an ohmic contact over the flexible substrate, an absorber layer over the ohmic contact, a window layer over the absorber layer, and a transparent conductive coating over the absorber layer.

11. The sensing device of claim 10, further comprising an antireflection coating between the absorber layer and the the transparent conductive coating.

12. The sensing device of claim 10, wherein the window layer comprises an n-type layer and the absorber layer comprises a p-type layer.

13. The sensing device of claim 10, wherein the window layer comprises cadmium sufide and the absorber layer comprises zinc telluride.

14. The sensing device of claim 9, wherein the sensing device further comprises a processor for sensing surface roughness of the leading edge of the wind blade by comparing a first current value generated by the photovoltaic layer with no deposition of airborne particles on the photovoltaic layer to a second current value generated by the photovoltaic layer during operation of the wind blade during similar sunlight conditions.

15. A method of operating a wind turbine; the method comprising:

sensing surface roughness on a leading edge of the wind blade by using a sensing device attached to the wind blade; and

controlling at least one operational parameter of the wind blade based on the sensed surface roughness of the wind blade to increase the operating efficiency of the wind turbine.

16. The method of claim 15, wherein the operational parameter comprises at least two operational parameters, and wherein the at least two operational parameters comprise a tip speed ratio and a pitch angle of the wind blade.

17. The method of claim 15, wherein the sensing device comprises an anemometer, a strain gauge, a photovoltaic sensor, or an optical sensor.

18. The method of claim 15, further comprising processing data sensed by the sensing device to determine a contamination level and determining values of the operational parameters based on the contamination level during operation of the wind blade.

19. The method of claim 15, further comprising, prior to installation of the sensing device on the leading edge, calibrating the wind blade to determine a contamination pattern of the wind blade due to deposition of airborne particles with respect to contamination of a location of the sensing device.

20. The method of claim 15, further comprising generating alerts for scheduling maintenance of the wind turbine based on the sensed surface roughness of the blade body.