The subject matter described herein relates generally to methods and systems for wind turbines, and more particularly, to methods and systems for damping oscillations of wind turbines.
At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to a generator by a shaft. A plurality of blades extend from the rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generator to generate electricity.
Oscillations of wind turbines, for example the periodic bending of the tower, can cause fatigue of wind turbine components, therefore systems and methods of reducing oscillations of wind turbines are implemented. Typically, systems and methods that reduce oscillations and associated fatigue of wind turbine components have disadvantages such as reducing annual energy production of wind turbines, or being costly. For example, methods to reduce oscillations of wind turbines can include forbidding the operation of the wind turbine at some operational frequencies that are near a natural frequency of the tower, which may reduce the risk of oscillation induced damage, but also compromise the energy production of the wind turbine.
In one aspect, a wind turbine is provided, including a rotor arranged at a nacelle, the nacelle supported by a tower, and a damper which includes a movable mass. The damper is adapted for variably adjusting a frequency response of the wind turbine.
In another aspect, a wind turbine is provided, including a rotor arranged at a nacelle, the nacelle supported by a tower, and a damper including a movable mass and a stiffness adjustment mechanism.
In yet another aspect, a method of operating a wind turbine is provided, including operating the wind turbine at an operational frequency; comparing the operational frequency to a reference frequency to form a comparison; and adjusting a damper according to the comparison.
Further aspects, advantages and features of the present invention are apparent from the dependent claims, the description and the accompanying drawings.
A full and enabling disclosure including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein:
Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations.
Embodiments described herein include a wind turbine that allows for greater annual energy production, reduced risk of fatigue and fatigue induced failure, reduced oscillations which can cause fatigue, and combinations thereof. Embodiments described herein result in a combined effect of allowing a wind turbine to operate within a broader range of operational frequencies, and at reducing undesirable frequency response of fatiguing periodic and/or oscillatory motion of the wind turbine, for example oscillations of the tower. By providing for an adjustable damper, the disadvantageous effects of previously forbidden operational frequencies which increased fatigue and increased the risk of fatigue induced failure, especially in comparison to previously allowed operational frequencies, are reduced and/or removed. By broadening the range of possible operational frequencies, energy production is increased, and without the deleterious effects of operating for example near resonance modes of the wind turbine, e.g. the tower's natural frequency of bending.
As used herein, the term “operational frequency” is intended to be representative of frequencies such as for example: the frequency of rotation of the rotor which is referred to as the 1 P frequency; the blade-passing frequency which may be referred to as the 3 P frequency in the case of 3-bladed rotors; and other harmonics such as 2 P, 4 P, 5 P and so on. Harmonics can be associated, although it is not necessary, with rotors with an arbitrary number of blades such as the 2 P frequency of a 2-bladed rotor. As used herein, the term “dashpot” is intended to be representative of an energy dissipating device, such as a viscous type dashpot, viscoelastic element, and/or eddy current damper. Herein the expression “more freely oscillating” is used interchangeably with “less damped.” Herein, “peak of response” is used interchangeably with “resonance peak” and “response peak” and can be synonymous with a “resonance,” As used herein, a “resonance” may have a width, or range of frequencies enveloping a response maximum and/or response peak, the resonance rising above the baseline of a response. Herein, a “natural frequency” can be an example of a resonance or resonance peak, and vice versa; “natural frequency” can refer to the natural frequency of the wind turbine, particularly a natural tower frequency, more particularly the first lateral bending frequency of the wind turbine or tower, although other oscillatory modes, particularly of the tower, are also contemplated. Herein, “stiffness” is used as meaning the inverse of “compliance” and vice versa. Alternatively or additionally, “stiffness” can relate to the mobility of a movable mass of a liquid, where more stiff corresponds to less mobility of the liquid. Herein, “forbidden” frequencies are intended to include frequencies, especially operational frequencies, that may normally lead to more fatigue, vibrations, and/or oscillations, for example of the tower. “Forbidden” frequencies are typical of frequencies at or near a resonance, such as the fundamental mode of the tower of the wind turbine. “Forbidden” frequencies can be operational frequencies that are seldom in operation, or are never in operation, or are less often in operation, for example in comparison to “allowed” frequencies. “Allowed” frequencies are intended to include frequencies that, in comparison to forbidden frequencies, may result in less fatigue, vibrations, and oscillations, for example of the tower. “Allowed” frequencies can be operational frequencies that are freely used in operation, or are more often used in operation than are forbidden frequencies. Herein, “damping” and “dampening” are used interchangeably. Herein, “locking” the damper can optionally be associated with increasing the stiffness of a component of the damper, such as the spring, dashpot, or combination of the two. Herein, a “damped wind turbine” is intended to mean a wind turbine with a damping system, which can damp motion in lateral and/or longitudinal directions. Herein, “frequency response” is intended to mean a frequency response of the tower, particularly in lateral and/or longitudinal directions of motion. Herein “movable mass,” “moving mass,” “second mass,” and/or “secondary mass” are used synonymously. Herein, the moving and/or movable mass can be a liquid. Herein, ranges can be continuous or discontinuous ranges.
As used herein, the term “blade” is intended to be representative of any device that provides a reactive force when in motion relative to a surrounding fluid. As used herein, the term “wind turbine” is intended to be representative of any device that generates rotational energy from wind energy, and more specifically, converts kinetic energy of wind into mechanical energy. As used herein, the term “wind generator” is intended to be representative of any wind turbine that generates electrical power from rotational energy generated from wind energy, and more specifically, converts mechanical energy converted from kinetic energy of wind to electrical power.
Rotor blades 22 are spaced about hub 20 to facilitate rotating rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. Rotor blades 22 are mated to hub 20 by coupling a blade root portion 24 to hub 20 at a plurality of load transfer regions 26. Load transfer regions 26 have a hub load transfer region and a blade load transfer region (both not shown in
In one embodiment, rotor blades 22 have a length ranging from about 15 meters (m) to about 91 m. Alternatively, rotor blades 22 may have any suitable length that enables wind turbine 10 to function as described herein. For example, other non-limiting examples of blade lengths include 10 m or less, 20 m, 37 m, or a length that is greater than 91 m. As wind strikes rotor blades 22 from a direction 28, rotor 18 is rotated about an axis of rotation 30. As rotor blades 22 are rotated and subjected to centrifugal forces, rotor blades 22 are also subjected to various forces and moments. As such, rotor blades 22 may deflect and/or rotate from a neutral, or non-deflected, position to a deflected position.
Moreover, a pitch angle or blade pitch of rotor blades 22, i.e., an angle that determines a perspective of rotor blades 22 with respect to direction 28 of the wind, may be changed by a pitch adjustment system 32 to control the load and power generated by wind turbine 10 by adjusting an angular position of at least one rotor blade 22 relative to wind vectors. Pitch axes 34 for rotor blades 22 are shown. During operation of wind turbine 10, pitch adjustment system 32 may change a blade pitch of rotor blades 22 such that rotor blades 22 are moved to a feathered position, such that the perspective of at least one rotor blade 22 relative to wind vectors provides a minimal surface area of rotor blade 22 to be oriented towards the wind vectors, which facilitates reducing a rotational speed of rotor 18 and/or facilitates a stall of rotor 18.
In the exemplary embodiment, a blade pitch of each rotor blade 22 is controlled individually by a control system 36. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by control system 36. Further, in the exemplary embodiment, as direction 28 changes, a yaw direction of nacelle 16 may be controlled about a yaw axis 38 to position rotor blades 22 with respect to direction 28.
In the exemplary embodiment, a damper 1, such as a damper for variably adjusting a frequency response of the tower and/or including a stiffness adjustment mechanism, is located near the top of the tower 12. Generally, the damper may be placed inside or outside the tower. The damper includes a movable mass.
In the exemplary embodiment, control system 36 is shown as being centralized within nacelle 16, however, control system 36 may be a distributed system throughout wind turbine 10, on support system 14, within a wind farm, and/or at a remote control center. Control system 36 includes a processor 40 configured to perform the methods and/or steps described herein. Further, many of the other components described herein include a processor. As used herein, the term “processor” is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and/or a control system can also include memory, input channels, and/or output channels.
In the embodiments described herein, memory may include, without limitation, a computer-readable medium, such as a random access memory (RAM), and a computer-readable non-volatile medium, such as flash memory. Alternatively, a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, input channels include, without limitation, sensors and/or computer peripherals associated with an operator interface, such as a mouse and a keyboard. Further, in the exemplary embodiment, output channels may include, without limitation, a control device, an operator interface monitor and/or a display.
Processors described herein process information transmitted from a plurality of electrical and electronic devices that may include, without limitation, sensors, actuators, compressors, control systems, and/or monitoring devices. Such processors may be physically located in, for example, a control system, a sensor, a monitoring device, a desktop computer, a laptop computer, a programmable logic controller (PLC) cabinet, and/or a distributed control system (DCS) cabinet. RAM and storage devices store and transfer information and instructions to be executed by the processor(s). RAM and storage devices can also be used to store and provide temporary variables, static (i.e., non-changing) information and instructions, or other intermediate information to the processors during execution of instructions by the processor(s). Instructions that are executed may include, without limitation, wind turbine control system control commands. The execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions.
Nacelle 16 also includes a yaw drive mechanism 56 that may be used to rotate nacelle 16 and hub 20 on yaw axis 38 (shown in
Forward support bearing 60 and aft support bearing 62 facilitate radial support and alignment of rotor shaft 44. Forward support bearing 60 is coupled to rotor shaft 44 near hub 20. Aft support bearing 62 is positioned on rotor shaft 44 near gearbox 46 and/or generator 42. Alternatively, nacelle 16 includes any number of support bearings that enable wind turbine 10 to function as disclosed herein. Rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and any associated fastening, support, and/or securing device including, but not limited to, support 52 and/or support 54, and forward support bearing 60 and aft support bearing 62, are sometimes referred to as a drive train 64.
In the exemplary embodiment, hub 20 includes a pitch assembly 66. Pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in
In the exemplary embodiment, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and to respective rotor blade 22 (shown in
Pitch drive system 68 is coupled to control system 36 for adjusting the blade pitch of rotor blade 22 upon receipt of one or more signals from control system 36. In the exemplary embodiment, pitch drive motor 74 is any suitable motor driven by electrical power and/or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, pitch assembly 66 may include any suitable structure, configuration, arrangement, and/or components such as, but not limited to, hydraulic cylinders, springs, and/or servo-mechanisms. Moreover, pitch assembly 66 may be driven by any suitable means such as, but not limited to, hydraulic fluid, and/or mechanical power, such as, but not limited to, induced spring forces and/or electromagnetic forces. In certain embodiments, pitch drive motor 74 is driven by energy extracted from a rotational inertia of hub 20 and/or a stored energy source (not shown) that supplies energy to components of wind turbine 10.
Pitch assembly 66 also includes one or more overspeed control systems 80 for controlling pitch drive system 68 during rotor overspeed. In the exemplary embodiment, pitch assembly 66 includes at least one overspeed control system 80 communicatively coupled to respective pitch drive system 68 for controlling pitch drive system 68 independently of control system 36. In one embodiment, pitch assembly 66 includes a plurality of overspeed control systems 80 that are each communicatively coupled to respective pitch drive system 68 to operate respective pitch drive system 68 independently of control system 36. Overspeed control system 80 is also communicatively coupled to sensor 70. In the exemplary embodiment, overspeed control system 80 is coupled to pitch drive system 68 and to sensor 70 with a plurality of cables 82. Alternatively, overspeed control system 80 is communicatively coupled to pitch drive system 68 and to sensor 70 using any suitable wired and/or wireless communications device. During normal operation of wind turbine 10, control system 36 controls pitch drive system 68 to adjust a pitch of rotor blade 22. In one embodiment, when rotor 18 operates at rotor overspeed, overspeed control system 80 overrides control system 36, such that control system 36 no longer controls pitch drive system 68 and overspeed control system 80 controls pitch drive system 68 to move rotor blade 22 to a feathered position to slow a rotation of rotor 18.
A power generator 84 is coupled to sensor 70, overspeed control system 80, and pitch drive system 68 to provide a source of power to pitch assembly 66. In the exemplary embodiment, power generator 84 provides a continuing source of power to pitch assembly 66 during operation of wind turbine 10. In an alternative embodiment, power generator 84 provides power to pitch assembly 66 during an electrical power loss event of wind turbine 10. The electrical power loss event may include power grid loss, malfunctioning of the turbine electrical system, and/or failure of the wind turbine control system 36. During the electrical power loss event, power generator 84 operates to provide electrical power to pitch assembly 66 such that pitch assembly 66 can operate during the electrical power loss event.
In the exemplary embodiment, pitch drive system 68, sensor 70, overspeed control system 80, cables 82, and power generator 84 are each positioned in a cavity 86 defined by an inner surface 88 of hub 20. In a particular embodiment, pitch drive system 68, sensor 70, overspeed control system 80, cables 82, and/or power generator 84 are coupled, directly or indirectly, to inner surface 88. In an alternative embodiment, pitch drive system 68, sensor 70, overspeed control system 80, cables 82, and power generator 84 are positioned with respect to an outer surface 90 of hub 20 and may be coupled, directly or indirectly, to outer surface 90.
In the exemplary embodiment, controller is a real-time controller that includes any suitable processor-based or microprocessor-based system, such as a computer system, that includes microcontrollers, reduced instruction set circuits (RISC), application-specific integrated circuits (ASICs), logic circuits, and/or any other circuit or processor that is capable of executing the functions described herein. In one embodiment, controller may be a microprocessor that includes read-only memory (ROM) and/or random access memory (RAM), such as, for example, a 32 bit microcomputer with 2 Mbit ROM, and 64 Kbit RAM. As used herein, the term “real-time” refers to outcomes occurring a substantially short period of time after a change in the inputs affect the outcome, with the time period being a design parameter that may be selected based on the importance of the outcome and/or the capability of the system processing the inputs to generate the outcome.
For example,
The damper 1 can be placed for example in the nacelle, attached to the nacelle, or placed in the tower or attached to the tower. For example, the damper can be placed in the upper portion of the tower, such as near the top of the tower. Typically, the damper 1 is more effective when it is placed as high as possible, which is typically near the top of the tower. For example, the damper is placed within a few percent of distance of the height of the tower from the top of the tower, for example more than 80% of the way to the top of the tower, or more than 90%, or more than 95%. The damper can be a passive, active, or semiactive tuned damper.
Optionally an additional damper can be located in the nacelle or near the top of the tower, and the additional damper can be oriented at 90 degrees from the first damper, for example to damp two dimensional oscillations (e.g. in two perpendicular directions), or even more. When two dampers are used, for example for damping motion in two perpendicular directions, they can be placed at equal height, for example near the top of the tower.
In an embodiment which may be combined with other embodiments, the damper 1 (which includes the second mass 610, the second spring 620, and the second optional dashpot 630) is adjustable, particularly to adjust the frequency response of the wind turbine.
For example,
In an embodiment, the stiffness adjustment mechanism is a component of the damper. Alternatively or additionally, the stiffness adjustment mechanism is a component of the wind turbine. Generally the stiffness adjustment mechanism restrains and/or blocks the motion of the movable mass 610. In an embodiment, which may be combined with other embodiments, the damper can be locked by the locking mechanism to increase stiffness, and unlocked to decrease stiffness.
An advantage of embodiments disclosed herein is that wind turbines including a damper that can variably adjust the frequency response of the wind turbine, for example effectively providing the third frequency response 700, can be operated throughout a larger range of frequencies, especially in comparison to a wind turbine with a response such as the first response 300 or a wind turbine with the second response 500. For example, a substantial fraction, most, or all of the low 710, middle 720 and high 730 frequency ranges are allowed for operation of a wind turbine with an adjustable damper, because operation of the wind turbine at frequencies with high responses which increase the risk of damage due to fatigue is avoided. The illustrated third frequency response 700 can be a combination of the first response 300 and second response 500.
In an embodiment, the damper 1 of a wind turbine 10 is locked by the locking mechanism 850 to increase stiffness and/or unlocked to decrease stiffness. For example, the wind turbine is operating at an operational frequency within the low range 710, according to the first response 300, and the damper is locked. As wind speed increases, the operational frequency increases, and to avoid operating the wind turbine near the maximum of the first resonance 300, the damper is unlocked so as to operate the wind turbine according to the second response 500 while the operational frequency is within the middle range 720. As the operational frequency possibly further increases, the damper can be again locked as the operational frequency increases to the high range 730.
For example, the damper is unlocked when the (increasing) operational frequency reaches the first intersection 750 of the first and second responses 300, 500. For example, the damper is locked when the (increasing) operational frequency reaches the second intersection 740 of the first and second responses 300, 500. For the opposite case, of decreasing operational frequency (e.g. going from the high range 730 through the middle and low ranges 720, 710) the unlocking and locking of the damper is performed in a similar manner to affect a more damped response. Typically, the selection of a response curve (i.e. switching between unlocked and locked) is at intersections of the frequency response curves, occurring so as to affect a lower response.
In an embodiment, the damper is locked by the locking mechanism 850 when the wind turbine is operated within a first range of operational frequencies (e.g. the first range includes the low 710 and high 730 ranges); and the damper may be unlocked by the locking mechanism when the wind turbine is operated within a second range of operational frequencies (e.g. the middle range 720 which is near the resonance of the wind turbine when the damper is locked).
According to an embodiment, which may be combined with other embodiments, the liquid is a movable mass. According to another combinable embodiment, the damper does not include a spring, rather utilizing gravitational force on the movable mass rather than the force of a spring.
Generally, the stiffness adjustment mechanism(s) may be a component of the damper, placed on an opposite side(s) of the tower from the damper(s), next to the damper(s), and/or symmetrically disposed around or within the tower.
For example, the operational frequency of a wind turbine with a locked damper is compared to a reference frequency such as an intersection of two response curves, e.g. the first intersection 750 (
In another example, two reference frequencies are utilized, e.g. the first and second intersections 750, 740 (
In another example, the operational frequency is compared to a natural frequency of the tower when the damper is locked. If the operational frequency is determined to be near the natural frequency of the tower in the locked condition (i.e. within the resonance peak, given its width), the damper is adjusted to be unlocked and/or its stiffness reduced. For example, the natural frequency is a frequency which has a response that is approximately 5%, 10%, 15%, 20%, 25% or 33% greater than the baseline of the frequency response of the wind turbine with, a locked damper. Alternatively or additionally, near the natural frequency can be within a range of frequencies around the resonance peak of the wind turbine with a locked damper, such as the envelope of frequencies that make up the resonance, having a width, which rises above the response baseline.
In an embodiment, which may be combined with other embodiments described herein, the controller is adapted to select the frequency response of the wind turbine for adjusting the damper. In yet another combinable embodiment, the variable stiffness of the damper is adjusted in correspondence with the variable adjustment of the frequency response of the wind turbine. In yet another combinable embodiment, the locking mechanism immobilizes the movable mass by activation of a piston, a valve, an inflatable stopper, or combinations thereof.
Embodiments described herein facilitate the one or more effects of: operating of a wind turbine at a wider range of operational frequencies, and reducing the risk associated with fatigue due to oscillations of wind turbine components, for example the bending motion of the tower. The systems and methods described herein thus increase energy production while providing for reduced risk of failure and/or damage. Embodiments described herein can provide allowed operational frequencies on and over the tower natural frequency. Furthermore, embodiments can: reduce the response at the tower natural frequency; allow the natural frequency of the tower to overlap the 1 P and 3 P ranges; no longer require curtailment at the two resonances that often or always result when a tuned mass damper is included in a wind turbine; extends the available frequency range; increases energy production (such as annual energy production); and/or saves costs of additional controllers and accelerometers of active tuned mass dampers.
Exemplary embodiments of systems and methods for wind turbines are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, dampers are not limited to practice with only the wind turbine systems as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other rotor blade applications.
Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. While various specific embodiments have been disclosed in the foregoing, those skilled in the art will recognize that the spirit and scope of the claims allows for equally effective modifications. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.