The invention generally relates to wind turbine and more particularly to wind turbine blade pitch control system.
BACKGROUND
Wind turbines with variable pitch system adjusts the angle of wind turbine blades to control the output power. The wind turbine includes a rotor having a hub mounted on a drive shaft and multiple blades are mounted on the hub. The blades transform wind energy into rotational motion of the drive shaft. The drive shaft in turn drives an electrical generator to produce electrical power to be fed to a power grid. During varying wind speed conditions, each of the multiple blades may pitch about a pitch axis, via blade pitch drive mechanisms, to maintain optimum RPM for power output and hence the electrical power produced by the electrical generator. The blade pitch system in wind turbines consists of a bearing on which the blade is attached. This bearing is joined by one part, i.e. the fixed or stationary part, to the hub, whilst the moving part is joined on one side to the blade and on the other side, the part located inside the hub, to a driving plate. The said blade, in turn, is connected, by means of a hydraulic or electric actuator, to the hub which makes the blade to rotate.
In a hydraulic system, hydraulic actuators control the pitch of blades. The actuator works against a spring/piston-cylinder that functions as a stop fail-safe upon loss of hydraulic pressure. The major drawback of the hydraulic system is the hydraulic fluid itself that results in the leakage problem. Additionally, the hydraulic systems tend to use more energy as the

An electric pitch-control system needs fail-safe batteries or supercapacitors to allow for loss of primary power or control. Fail-safe batteries typically last only two to three years, and then must be replaced, not a simple task as the fail-safe batteries sit in the hub of the rotor, not in the nacelle. Electric systems also work better in colder climes where the oil in hydraulic systems loses viscosity as the temperature drops.
Hence there is a need for an improved pitch control system for a wind turbine blade
SUMMARY OF THE INVENTION
According to an exemplary embodiment of the invention, a pitch control system for a wind turbine blade is disclosed. The wind turbine blade is mounted on a wind turbine hub. The pitch movement of the wind turbine blade with respect to the wind turbine hub is achieved through a bearing. The bearing may include a pair of rings such that one ring is concentrically arranged the other ring. According to an embodiment, the pitch control system includes at least one magnetic element coupled to each ring. The magnetic elements may be coupled to the respective rings through a plurality of studs. The arrangement of the magnetic elements in the pitch control system is such that at least one magnetic element may be selectively excited to produce a magnetic flux having a polarity opposite to the polarity of the other magnetic element on the other ring. The excitation of the magnetic element is managed to control the pitch of wind turbine blade.
BRIEF DESCRIPTION OF DRAWINGS

Other objects, features, and advantages of the invention will be apparent from the following description when read with reference to the accompanying drawings. In the drawings, wherein like reference numerals denote corresponding parts throughout the several views:
Figure 1 illustrates an isometric view of a wind turbine hub with a pitch control system for one wind turbine blade according to an exemplary embodiment of the invention.
Figure 2 illustrates an exploded view of a pitch control system according to an exemplary embodiment of the invention.
Figure 3 illustrates a cross sectional view of a pitch control system according to an exemplary embodiment of the invention.
Figure 4 illustrates the working arrangement of the pitch control system according to an exemplary embodiment of the invention.
DETAILED DESCRIPTION OF DRAWINGS
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skilled in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the
scope and spirit of the invention. In addition, descriptions of well-known functions and
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Figure 1 illustrates an isometric view of a wind turbine hub 102 with a pitch control system 100 for one wind turbine blade according to an exemplary embodiment of the invention. The figure 1 shows a cut-out section of a component in the wind turbine hub 102 for better understanding of the invention. The pitch control system 100 enables a wind turbine blade to pitch in response to the speed of the wind. The pilch movement of the wind turbine blade not only adjusts the angle of blade to turn a rotor efficiently, but also protects the blade from damage due to excessive wind forces. The wind turbine hub 102 includes at least one opening for mounting a bearing, the pitch control system 100 and the wind turbine blade on it. The wind turbine blade is mounted on the wind turbine hub 102 through the bearing. The bearing enables the wind turbine blade to rotate freely on its axis on to the wind turbine hub 102. The bearing may include a pair of rings 104, 106, one ring 104 arranged concentrically to the other ring 106. One of the ring may be an outer ring 104 and the other ring may be an inner ring 106. The outer ring 104 of the bearing may be coupled to the periphery of the hub 102 opening and therefore the outer ring 104 may be stationary. The inner ring 106 of the bearing may be coupled to a root of the wind turbine blade and may freely rotate with respect to the outer ring 104 through a plurality of balls 116. According to an embodiment, the bearing between the wind turbine hub 102 and the wind turbine blade may be a ball bearing. According to another embodiment, the bearing between the wind turbine hub 102 and the wind turbine blade may be a roller bearing.
Figure 2 illustrates an exploded view of a pitch control system 100 according to an exemplary
embodiment of the invention. The pitch control system 100 may include at least one magnetic
element 108, 110 coupled to each of the rings 104, 108. According to an embodiment, the
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magnetic elements 108, 110 may be a permanent magnet. According to yet another embodiment, one magnetic element 108 may be an electromagnet and the other magnetic element 110 may be a permanent magnet. According to yet another embodiment the magnetic elements 108, 110 may form a magnetic bearing. Each magnetic element 108, 110 may be coupled to a separate ring 104, 106. According to an embodiment, the magnetic element 108 being coupled to the outer ring 104 may be substantially similar in shape and size of the outer ring 104. According to another embodiment, the shape and size of the magnetic element 104 may be different to the shape and size of the outer ring 104. According to an embodiment, the magnetic element 110 being coupled to the inner ring 106 may be substantially similar in shape and size of the inner ring 106. According to another embodiment, the shape and size of the magnetic element 110 may be different to the shape and size of the inner ring 106. As shown in figure 1, the magnetic elements 108, 110 may be located inside the wind turbine hub 102 and coupled to the inside surface of the respective rings 104, 106. According to an embodiment, the magnetic elements 108, 110 may be coupled to the rings 104, 106 through a plurality of studs 114. According to another embodiment, the magnetic elements 108, 110 may be coupled to the rings 104, 106 through a plurality of bolts. According to yet another embodiment, the magnetic elements 108, 110 may be coupled to the rings 104, 106 by any fastening means. The magnetic elements 108, 110 may be coupled to the rings 104, 106 in such a way that the magnetic elements 108, 110 may be detachable from the ring 104, 106 for servicing requirements.
Figure 3 illustrates a cross sectional view of a pitch control system 100 according to an
exemplary embodiment of the invention. The bearing between the wind turbine hub 104 and
the wind turbine blade includes the outer ring 104 and the inner ring 106. According to an
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between them. According to another embodiment, the outer ring 104 and the inner ring 106 may include a plurality of rollers in between them. The bearing between the wind turbine hub 104 and the wind turbine blade may be of any type such as, but not limited to, a deep groove ball bearing, an angular contact ball bearing, a thrust roller bearing, a spherical roller bearing, a tapered roller bearing, a cylindrical roller bearing etc. The magnetic elements 108, 110 may be coupled to the respective rings 104,106 through a detachable fastening means. According to an embodiment, the magnetic element 108 on one ring 104 may be separated to the magnetic element 110 on the other ring 106 by an air gap. The air gap may between the magnetic elements 108, 110 may prevent the wear and tear of the magnetic elements 108, 110 connected to each of the rings 104, 106. The pitch control system 100 may further include at least one plate 112 on each side of the magnetic elements 108, 110 to enclose the air gap between the magnetic elements 108, 110. The plates 112 may protect the air gap from foreign particles such as, but not limited to dust, water, bolts, wind turbine components etc and therefore may enable smooth working of the magnetic elements 108, 110.
Figure 4 illustrates the working arrangement of the pitch control system 100 according to an exemplary embodiment of the invention. The wind turbine blade coupled to the inner ring 106 may be at a certain orientation along the pitch axis. According to an embodiment, the magnetic element 110 coupled to the inner ring 106 may be a permanent magnet having a magnetic polarity and the magnetic element 108 coupled to the outer ring 104 may include at least a pair of electromagnets arranged diametrically opposite to each other. According to another embodiment, the magnetic element 110 coupled to the inner ring 106 may include at least a pair of electromagnets arranged diametrically opposite to each other and the magnetic element 108 coupled to the outer ring 104 may be a permanent magnet having a magnetic polarity. The E- ^rhagnetifelementSoS hating &le^tro*nagnefi may fee-sefeetivilV excite1 dfo:produce a magnetic

flux having a magnetic polarity. When the magnetic element 108 produces a magnetic flux, the magnetic element 110 coupled to the inner ring 106 may rotate due to rotational magnetic field, causing the pitch movement of the wind turbine blade. According to an embodiment, the pitch control system 100 may include a sensor 118 to determine the orientation of the wind turbine blade. The sensor 118 for identifying the pitch blade orientation may be a position sensor. The sensor 118 may send the information regarding the orientation of the wind turbine blade to a controller 120. The controller 120 may control flow of current from a current source to the magnetic element 108 having electromagnets. The current from the current source may cause the excitation of the magnetic element 108. The pitch control system 100 may further include a system to restrict the motion of the bearing within 0 to 100 degrees. The system may lock the movement of the bearing by a mechanical system.
It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein," respectively.

1. A pitch control system 100 for a wind turbine blade, the blade being mounted on a
wind turbine hub 102 through a bearing, the bearing having a pair of concentric rings
104, 106, the pitch control system 100 comprising:
at least one magnetic element 108, 110 being coupled to each ring 104, 106, such that at least one magnetic element 108, 110 being selectively excited to provide a magnetic flux having a polarity opposite to the polarity of the magnetic element 108, 110 on the other ring 104, 106 thereby controlling the pitch of wind turbine blade.
2. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the magnetic elements 108, 110 are coupled to respective rings 104, 106 through a plurality of studs 114.
3. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the magnetic elements 108, 110 are coupled to respective rings 104, 106 through a plurality of bolts 114.
4. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the bearing includes a plurality of balls 116 in between the concentric rings 104, 106.

5. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the bearing includes a plurality of rollers 116 in between the concentric rings 104, 106.
6. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the magnetic element 108 on one ring 104 may be separated to the magnetic element 110 on the other ring 106 by an air gap.
7. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the pitch control system 100 further includes at least one plate 112 on each side of the magnetic elements 108, 110 to protect the air gap between the magnetic element 108 and the magnetic element 110.
8. The pitch control system 100 for the wind turbine blade as claimed in claim 1, wherein the pitch movement of the wind turbine blade is restricted between 0 to 100 degrees.