Patent Application
20130343887
The present disclosure relates generally to wind turbines and, more particularly, relates to variable speed friction wheel drive trains for wind turbines.
A utility-scale wind turbine typically includes a set of two or three large rotor blades mounted to a rotor hub. The rotor blades and the rotor hub together are referred to as the rotor. The rotor blades aerodynamically interact with the wind and create lift and drag, which is then translated into a driving torque by the rotor hub. The rotor is attached to and drives a main shaft, which in turn is operatively connected via a drive train to a generator or a set of generators that produce electric power. The main shaft, the drive train and the generator(s) are all situated within a nacelle, which is situated on top of a tower.
Many types of drive trains are known for connecting the main shaft to the generator(s). One type of drive train uses various designs and types of speed increasing gearboxes to connect the main shaft to the generator(s). Typically, the gearboxes include one or more stages of gears and a large housing, wherein the stages increase the rotor speed to a speed that is more desirable for driving the generator(s). While effective, large forces translated through the gearbox can deflect the gearbox housing and components therein and displace the large gears an appreciable amount so that the alignment of meshing gear teeth can suffer. When operating with misaligned gear teeth, the meshing teeth can be damaged, resulting in a reduced lifespan. The large size of these gearboxes and the extreme loads handled by them (including transient over torque conditions) make them even more susceptible to deflections and resultant premature wear and damage, such as gear pitting. Furthermore, maintenance and/or replacement of parts of damaged gearboxes may not only be difficult and expensive, it may require entire gearboxes to be lifted down from the wind turbine.
To counteract the disadvantages of traditional gearboxes, some wind turbines have started employing friction wheel drive trains. Friction wheel drive trains replace conventional gearboxes in a wind turbine and include at least one drive wheel and at least one driven wheel as speed increasing stages that drive the generator(s) connected thereto. Motion in friction wheel drive trains is transmitted from the drive wheel to the driven wheel through frictional forces. While the friction wheel drive train alleviates at least some of the problems associated with conventional gearboxes, the friction wheel drive trains that are employed currently are constant speed ratio drive trains.
With such constant speed ratio drive train friction wheel systems, the rotational speed of the generator(s) connected to the driven wheel of the friction wheel drive train varies as the wind turbine rotational speed varies (in variable speed wind turbines). As the speed of the generator(s) varies, the output frequency of the generator(s) varies as well. In order to transmit the generator power to a grid, a fixed frequency alternating current (AC) wave form must be produced by the generator(s) and synchronized to the grid. With variable speed wind turbines employing constant speed ratio friction wheel drive trains and variable frequency generator(s), a fixed output frequency of the generator(s) is typically accomplished by first rectifying the generator output power (from AC) to direct current (DC) power. This DC power is then inverted to create a fixed AC wave form. The power electronic equipment utilized to rectify and invert the wind turbine generator output power is not only expensive, it is also inefficient and unreliable. An alternative to using variable speed wind turbines is a fixed rotational speed wind turbine in which the rotational speed of the rotor (and therefore the generators) does not change. However, fixed rotational speed wind turbines are not very desirable, given specially that they are aerodynamically less efficient than variable speed wind turbines.
Accordingly, it would be beneficial if a friction wheel drive train were developed that could alleviate at least some of the disadvantages of conventional gearboxes while providing a capability to regulate an output frequency of variable frequency generator(s) and synchronize the generator(s) with the grid without any special power electronic component in variable speed wind turbines.
In accordance with one aspect of the present disclosure, a drive train for a wind turbine is disclosed. The drive train may include at least one drive wheel adapted to receive mechanical energy from a main shaft of a wind turbine and capable of rotating at a variable input rotational speed and at least one driven wheel in at least indirect contact with the at least one drive wheel, the at least one driven wheel capable of at least indirectly translating against the at least one drive wheel to vary a speed ratio of the drive train to provide a constant output rotational speed.
In accordance with another aspect of the present disclosure, a wind turbine is disclosed. The wind turbine may include a hub, a plurality of blades radially extending from the hub and a main shaft rotating with the hub. The wind turbine may also include a drive train comprising (a) at least one drive wheel mounted to the main shaft and rotating at a variable input rotational speed; and (b) at least one driven wheel in at least indirect contact with the at least one drive wheel, the at least one driven wheel capable of providing a constant output rotational speed by varying a speed ratio of the drive train.
In accordance with yet another aspect of the present disclosure, a method of varying a speed ratio of a drive train for a wind turbine is disclosed. The method may include providing a drive train having (a) at least one drive wheel mounted to a main shaft of a wind turbine and rotating at a variable input rotational speed; and (b) at least one driven wheel in at least indirect contact with the at least one drive wheel, the at least one driven wheel capable of providing a constant output rotational speed. The method may also include translating the at least one driven wheel at least indirectly against a surface of the at least one drive wheel and changing a contact location between the at least one drive wheel and the at least one driven wheel during the translating step to vary the speed ratio of the drive train.
Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.
For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein:
While the following detailed description has been given and will be provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims eventually appended hereto.
Referring now to
In addition to the components of the wind turbine 2 described above, the up tower section 4 of the wind turbine may include several auxiliary components, such as, a yaw system 26 on which the nacelle 16 may be positioned to pivot and orient the wind turbine in a direction of the prevailing wind current or another preferred wind direction, a pitch control unit (PCU) (not visible) situated within the hub 12 for controlling the pitch (e.g., angle of the blades with respect to the wind direction) of the blades 10, a hydraulic power system (not visible) to provide hydraulic power to various components such as brakes of the wind turbine, a cooling system (also not visible), a lightning rod 28 for protecting the wind turbine from lightning strikes, and the like. Notwithstanding the auxiliary components of the wind turbine 2 described above, it will be understood that the wind turbine 2 may include several other auxiliary components that are contemplated and considered within the scope of the present disclosure. Furthermore, a turbine control unit (TCU) 30 and a control system 32 (one or both of which may be classified as auxiliary components) may be situated within the nacelle 16 for controlling the various components of the wind turbine 2.
With respect to the down tower section 6 of the wind turbine 2, among other components, the down tower section may include a pair of generator control units (GCUs) 34 and a down tower junction box (DJB) 36 for routing and distributing power between the wind turbine and the grid. Notwithstanding the fact that in the present embodiment, a pair of the GCUs 34 has been shown, in at least some embodiments, the number of the GCUs may vary from a single unit to possibly more than two as well. In addition, several other components, such as, ladders, access doors, etc., that may be present within the down tower section 6 of the wind turbine 2 are contemplated and considered within the scope of the present disclosure.
Referring now to
Notwithstanding the fact that in the present embodiments, the drive train 18 has been shown as being a single stage speed increaser, in at least some other embodiments, the drive train 18 may be a multi-stage variable speed ratio speed increaser that employs multiple sets of the drive wheel 38 and the driven wheels 40. For example, for a two stage speed increaser, the drive wheel 38 may drive the driven wheels 40, which in turn may be connected to another one of the drive wheel (e.g., the driven wheels may be sandwiched between two drive wheels) and that drive wheel may drive another set of driven wheels. Depending upon the number of stages of speed increase desired, the number of the stages (each stage having one set of the drive wheel and the driven wheels) of the drive wheel 38 and the driven wheels 40 may vary as well. In addition, although in the present embodiment, only a single drive wheel 38 that drives the plurality of driven wheels 40 has been shown, this is merely exemplary. In other embodiments, more than one of the drive wheel 38 driving a single or multiple number of the driven wheels 40 may be employed. Similarly, one or more of the drive wheel 38 driving a single one of the driven wheels 40 may be used as well.
Additionally, the drive wheel 38 and the driven wheels 40 may be constructed of any of a variety of commonly employed materials in friction wheels. For example, in some embodiments, one or both of the drive wheel 38 and the driven wheels 40 may be constructed of steel (e.g., polished steel or machined steel). While constructing the drive and the driven wheels 38 and 40, respectively, of steel may advantageously transmit power from the drive wheel to the driven wheels with greater efficiency, in at least some other embodiments, one or both of the drive and the driven wheels may be constructed of other materials, such as, rubber, wood or possibly plastic. In yet other embodiments, depending upon the efficiency, wheel life span, cost and power requirements that are desired, other types of materials may be employed as well for constructing one or both of the drive wheel 38 and the driven wheels 40.
With respect to the size of the drive wheel 38 and the driven wheels 40, it may vary as well, depending particularly upon the speed ratio of the drive train 18 that is desired. As stated above, the drive train 18 (e.g., the friction wheel drive train) is a variable speed ratio speed increaser friction wheel, meaning that the drive train is capable of increasing (or decreasing) the rotational speed of the rotor 8 to provide a constant output rotational speed for driving the one or more generators 20. In other words, the drive train 18 and particularly, the driven wheels 40 may be capable of supplying a constant output rotational speed, independent of the input rotational velocity of the main shaft 14 that drives the drive wheel 38. Thus, depending upon the ratio of the input rotational speed to the output rotational speed (also referred to herein as speed ratio) that is desired, the size of the drive wheel 38 and the driven wheels 40 may vary in order to provide a constant output rotational speed for a given input rotational speed. Generally speaking, by varying the effective circumference of the drive wheel 38 and the driven wheels 40 and the area (and/or location) of contact therebetween, a desired speed ratio may be obtained. The shape of the drive wheel 38 and/or the driven wheels 40 may vary as well, as described further below.
Referring still to
In operation, when the drive wheel 38 is rotated by the wind turbine 2 (e.g., by the rotor 8 and the main shaft 14), and the driven wheels 40 are forced (e.g., rotated and/or translated) against the drive wheel, rotational motion from the drive wheel is transferred to the driven wheels and torque from the drive wheel is split into multiple pathways to the driven wheels. For an “X” number of the driven wheels 40 that may be employed for each one of the drive wheel 8, the torque may be split into “X” number of pathways. By splitting torque, a reduction of the overall forces on the main shaft 14 that are reacted by main shaft bearings may be achieved. Reducing forces required to be reacted by the main shaft bearings is important in ensuring the longevity of the drive train 18 and/or reducing the cost of the bearings. Furthermore, by rotating and/or translating the driven wheels 40 against the drive wheel 38, an increase or decrease in the desired speed ratio may be achieved, thereby providing a variable speed ratio speed increaser.
For example, for a desired generator speed that is about ten (10) times the speed of the rotor 8, the size of the driven wheels 40 may be selected to be nominally about ten (10) times smaller than the drive wheel 38. The nominal size of both the drive wheel 38 and the driven wheels 40 may be measured at the average diameter of the respective wheel. As the rotational speed of the rotor 8 falls below its nominal rated speed, the generator speed may begin to proportionally decrease. To mitigate the generator speed reduction, the speed ratio of the drive train 18 may be increased by translating the driven wheels 40 against the drive wheel 38, until the generator speed accelerates to its desired operating speed. Relatedly, if the rotational speed of the rotor 8 climbs above its nominal rated speed, the generator speed may begin to proportionally increase. To mitigate the generator speed increase, the speed ratio of the drive train 18 may be decreased by translating the driven wheels 40 against the drive wheel 38, until the generator speed decelerates to its desired operating speed. Thus, by translating the driven wheels 40 and the drive wheel 38 relative to one another, a constant rotational speed of the generators 20 may be achieved. Various embodiments of varying (e.g., increasing or decreasing) the speed ratio are described below in
Referring specifically now to
Furthermore, the drive wheel 38 may be a flat circular disk rotating in a direction shown by an arrow 44 and having an inner wall 46 (e.g., defining an inner radius, as measured from a center of the disk), an outer wall 48 (e.g., defining an outer radius that is larger than the inner radius) and a front surface 50 extending between the inner and the outer walls. Each of the driven wheels 40, which may be smaller in radius than the drive wheel, may be rotating in a direction indicated by arrows 52. Notwithstanding the particular directions of rotation of the drive and the driven wheels 38 and 40, respectively, that has been shown, this is merely exemplary. The direction of rotation of the drive wheel 38 and the driven wheels 40 may vary in other embodiments. For example, the drive wheel 38 and the driven wheels 40 may both rotate in the same direction (clockwise or counter clockwise) or they may rotate in opposite directions as well.
In addition, the driven wheels 40 may be arranged symmetrically about the drive wheel 38 and the main shaft 14 in such a way that a rotational axis of each of the driven wheels is not coaxial with a rotational axis of the drive wheel. By virtue of arranging the driven wheels 40 non-coaxially about the drive wheel 38 and the main shaft 14, the driven wheels may be translated against the drive wheel in a manner described below to vary the contact location and the effective circumference of the drive wheel and the driven wheels to vary the speed ratio. Translation of the driven wheels 40 with respect to the drive wheel 38 may be achieved by any of variety of mechanical or electromechanical devices, such as, a hydraulic ramp, a rack and pinion, a ball screw, a slider crank, or any other actuator capable of facilitating a linear motion (in case of flat disks) and/or traversing a convex or concave path, via a curved path of motion (in case of concave or convex disks). Furthermore, as shown in
In order to increase the overall speed ratio of the drive train 42, each of the driven wheels 40 (and the generators 20 connected thereto) may be translated radially outward about the front surface 50 of the drive wheel 38 in a direction shown by arrow 56 in
Relatedly, as shown in
It will be understood that each of the driven wheels 40 may translate at different speeds (and different directions) and up to a different level, depending upon the output rotational speed required to maintain the output frequency of the generator 20 connected to a particular one of the drive wheel. In other words, some of the driven wheels 40 may be translated to increase the speed ratio while some of the driven wheels may be translated to decrease the speed ratio, depending upon the requirements of the generators 20 connected thereto.
Turning now to
In contrast to the drive wheel 38 of
Furthermore, the driven wheels 40 may be translated with respect to the drive wheel 38 between the inner and the outer walls 66 and 68, respectively, of the driven wheels to increase or decrease the speed ratio of the drive train 60. For example, and as shown in
Turning now to
The drive wheel 38 in
The driven wheels 40 may further be arranged such that the outer sloping surface 88 of the driven wheels contacts the outer sloping surface 82 of the driving wheels, which may be translated axially about the drive wheel. As shown in
Referring now to
Accordingly and as shown in the cross-sectional views of
In order to increase the overall speed ratio of the drive train 94, as shown in
As with the embodiments of
Turning now to
By virtue of utilizing the translatable idler wheel 108 between each of the driven wheels 40 and the drive wheel 38, only the translatable idler wheel needs to translate. The driven wheels 40 and the generators 20 may remain stationary. Advantageously, by avoiding the need to translate the generators 20, the design and complexity of the generators (and the extra cabling used to account for the translation) may be reduced. It will be understood that while the translatable idler wheels 108 have been shown with respect to the embodiment of
Thus, the outer sloping surface 88 of the driven wheels 40 contacts an outside diameter 110 of one of the translatable idler wheels 108, which in turn contacts the outer sloping surface 82 of the drive wheel 38. As shown in
Relatedly, as shown in
Thus, the present disclosure sets forth a variable speed ratio friction wheel speed increaser drive train that employs at least one drive wheel and at least one driven wheel to provide a constant output rotational speed independent of the input rotational speed of the rotor of the wind turbine. Motion from the at least one drive wheel is transmitted to the at least one driven wheel through frictional forces. Furthermore, the at least one driven wheels may be translated along a surface of the at least one drive wheels in order to vary the speed ratio. Although the above embodiments have been described with the at least one driven wheels translating against a fixed one of the at least one drive wheel, in at least some embodiments, the at least one driven wheels may be fixed in position and the at least one drive wheel may translate against the fixed ones of the at least one driven wheels to change the speed ratio.
By providing a variable speed ratio drive train, such as the one described above, use of a synchronous generator design within a wind turbine may be facilitated. This variable speed ratio speed increaser may produce a constant output rotational velocity, independent of the wind turbine shaft rotational velocity to regulate the output frequency and power of the generators connected to the a least one driven wheels. The variable speed ratio speed increaser friction wheel drive train may, thus, allow a wind turbine manufacturer to eliminate the expensive power electronics that are required with variable speed generators that are driven by a constant ratio speed increaser drive trains.
While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.
