Patent Application
20110044811
The present disclosure relates to a wind turbine, and more particularly to wind turbines designed for optimum performance when maintained in a particular orientation relative to wind direction.
Active systems have been employed to trim a wind turbine in yaw to maintain a desired orientation. A controller of the active system maintains the angle between the wind direction and the rotational axis of the rotor, i.e. the axis of the rotor shaft, at a predetermined value. As the wind direction changes, the controller directs yaw actuation motors to rotate the nacelle into a desired angle with respect to the wind. For effective controller operation, the instantaneous direction of the wind must be known accurately. Therefore, it is common to mount a wind-direction indicator to the top of the nacelle to measure wind direction. This approach may have several complicating issues.
The wind direction felt by the wind-direction indicator may be distorted by the passage of the blades, especially for the common layout that places the rotor up-wind of the nacelle. Also, the wind-direction is measured at a single point in space, which, in the presence of atmospheric turbulence, may cause the indicated wind direction to depart from the desired rotor-averaged value. Furthermore, the wind-direction indicator, being mounted externally and above, the nacelle, is subjected to force majeure events from the weather, such as gale-force winds and lighting strikes. Lastly, the passage of the blades may cause a periodic, “fish-tail,” motion of the wind-direction indicator which may, over time, result in mechanical fatigue and lubrication issues that may result in measurement errors due to friction and other undesired mechanical effects.
A method of wind turbine control includes determining wind tangential velocity, averaged over a rotor swept plane, from an instantaneous measurement of a rotor azimuth angle and a rotor teeter angle to control a wind turbine yaw angle.
A method for measuring the tangential wind velocity, averaged over a rotor swept area of a wind turbine includes measuring the instantaneous yaw rate, the instantaneous rotor azimuth angle, and the instantaneous blade “out-of-mean-plane” angle. Storing the teeter angle over at least one complete rotation of the rotor. Fourier decomposing the angle β(ψ) into the mean value and harmonics in ψ. Measuring the wind shear rate at a location adjacent to the wind turbine. Measuring the rotor-averaged axial wind component. Using a governing equation of motion for the rotor to recover the tangential wind component.
A wind turbine includes a nacelle rotationally attached to the tower for rotation about a yaw axis. A rotor rotationally mounted to the nacelle through a teeter hinge system. A yaw drive system operable to adjust a yaw-angle of the nacelle about the yaw axis. A sensor system operable to measure at least one quantity of said rotor. A module in communication with the sensory system, the module operable to measure wind direction to control said yaw drive system.
Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:
The rotor 24 includes a hub 30 having a multiple of blades 32 which rotate through an azimuth angle ψ (
The hub 30 is supported upon a slow speed shaft 34 which rotates about an axis of rotation A to drive at least one generator 36 contained in the nacelle 26. The nacelle 26 is rotationally attached to the tower 22 through a yaw bearing 38 to define a yaw angle α. The entire tower-top assembly, i.e. the components above the yaw bearing 38 may be rotated about the yaw axis Z through at least one yaw drive system 40 (illustrated schematically).
For a two-bladed, teetered rotor 24, the dynamic motion of the rotor blades 32, in particular the teeter angle β is utilized to deduce the wind-direction, averaged over the rotor plane. The deduction includes measurements of other factors which affect the teeter angle β with a dynamic equation of motion to deduce the wind direction. The measurement of wind direction, averaged over the entire swept area of the rotor 24 is utilized for wind turbine control rather than the conventional extrapolated wind direction averages from a single point measurement. Such a measurement in which the rotor itself is the sensor provides a more robust system against environmental factors.
Referring to
The module 50 typically includes a processor 54A, a memory 54B, and an interface 54C. The processor 54A may be any type of known microprocessor having desired performance characteristics. The memory 54B may, for example only, include UVPROM, EEPROM, FLASH, RAM, ROM, DVD, CD, a hard drive, or other computer readable medium which stores the data and control algorithms described herein. The interface 54C facilitates communication with a sensor system 56 as well as other systems. The module 50 and the sensor system 56 provide a wind-direction system 58 for the wind turbine 20.
Referring to
Referring to
The wind velocity varies with spatial location and time. As such, the desired value is wind averaged velocity, which is wind velocity averaged over the swept-area of the rotor 24. Wind averaged velocity
The disclosure provides for the measurement of the tangential wind velocity
The governing equation is utilized to extract the tangential wind velocity from the measured quantities. A convenient equation to use, for example, is the linearized form of the equation governing the instantaneous teeter angle β. For the case that the Fourier expansion of the teeter angle β (ψ) is limited to the first harmonic:
β=β0+β1c cos(ψ)+β1s sin(ψ) (1)
The linearized form of the equation is:
Where:
A detailed description of each term can be found in chapter 4 of “Wind Energy Explained” by J. F. Manwell, J. G. McGowan and A. L. Rogers, Wiley Publishers, 2002. Equations for the higher harmonics of β are well known in the art and can be included to increase the accuracy of this disclosure. In the case of individually hinged blades, the equations of motions refer to the flapping degrees of freedom β0; β1s; β1c of each blade as is well known in the art.
Equation 3 relates the wind tangential direction,
The disclosure herein describes use of the governing equations of motion, together with a measurement of other quantities, namely yaw rate, wind shear and axial wind velocity that affect teeter angle β to deduce the tangential wind velocity
The yaw rate q is a mechanical motion of the wind turbine 20 about axis Z, and can be readily measured; the wind shear rate Kvs is measurable by a multitude of methods known in the art, including Light Detection and Ranging (LIDAR) and Sonic Detection and Ranging (SODAR) devices based on light and sound modification due to air motion, respectively, as well as a series of anemometers placed at different heights above the ground. The wind shear exponent Kvs changes slowly with location around the wind turbine 20, as well as time of day, and a single measurement along a single vertical line provides a good representation of the value over the entire rotor swept area; and the value of the axial wind component, averaged over the rotor plane, manifests itself in the instantaneous generator power, when the generator is below rated speed, or in the yaw angle (2-bladed rotors, aerodynamic power control through active yaw) or collective blade pitch (rotors with pitch-controlled blades), when above rated speed. It is, therefore, also readily measurable.
In formula 3, the wind-shear, the rotor azimuth, the teeter angle and the yaw rate are combined to deduce the instantaneous value of
In the case of individually hinged blades, the equation for V0 has an expanded form relative to formula (3), wherein the instantaneous hinge angles β0, β1s, . . . of each blade appear. To recover the mean β0 and harmonics β1s and β1c from the measured teeter angle β, the signal history β(ψ) (i.e. as function of rotor azimuth position), is stored in a finite-length array in bucket-brigade format, i.e., newest sample in, oldest sample out. The array as a length of a multiple of 2π radians permits evaluation of β0; β1s; β1c via a Fourier transform. This transform may be performed after each new sample is added to the array, which thereby provides the instantaneous values of the desired quantities.
In operation and with reference to
It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.
The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.
