Patent Application
20110206515
The subject matter described herein relates generally to methods and systems for the yaw adjustment of wind turbines, and more particularly, to methods and systems for the hydraulic yaw adjustment 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.
If the plane defined by the rotor blades of the wind turbine is not perpendicular to the wind, the turbine may still be operable, but the rotor blades and the nacelle, to which they are coupled via the rotor blade hub and the rotor axis, experience shear forces that lead to a large load on these parts, to wear, and, hence, to an increased need for maintenance. Typically, the nacelle, to which the rotor is connected, is therefore turned to directly face the wind. To this aim, a controller, such as an electronic computer, receives measurement data of wind direction and wind speed and controls a motor to accordingly adjust a yaw angle of the nacelle.
Typically, the at least one motor is an electric motor, which turns the nacelle via a gear with a high transmission ratio. If the wind changes direction, the nacelle is turned accordingly by the yaw drive system, until the plane of the rotor is again perpendicular to the direction of the wind. During this process, as long as the rotor plane is not perpendicular to the wind direction, the wind will exhibit shear forces on the nacelle which may contravene the force of the yaw drive motor. If a gust hits the wind turbine during this process, the yaw drive system, and particularly the yaw motor, has to withstand particularly high forces.
Hence, the maximum exertable torque of the yaw drive motor has to be adapted such that the yaw drive system may exert a torque on the nacelle which is higher than the torque that the rotor exerts on the nacelle during strong gusts or other cases with extreme load. The torque which the yaw motor or motors have to produce to move the nacelle during a gust is considerably higher than the torque that is needed for the adjustment of the yaw angle under normal operating conditions. In extreme cases, the torque exerted on the yaw motor can be four to five times as high as the torque which is needed to adjust the yaw angle under standard operating conditions.
Further, the gear components of the yaw drive system also have to be designed to withstand these high gust forces. Together, these factors require a considerable oversizing of the motor and gear of conventional yaw drive systems, which is an undesired cost factor.
Accordingly, it is desirable to have a yaw drive system which is designed to exhibit a maximum torque which is sufficient for the adjustment of the yaw angle under normal operating conditions, but has a lower maximum torque than conventional yaw systems and is suitable to react on high torque caused by gusts without suffering damage or without further unwanted side effects.
In one aspect, a yaw drive system for a wind energy system is provided. The system includes a hydraulic yaw motor for adjusting the yaw angle of a nacelle of a wind energy system, at least one hydraulic pump adapted for providing a pressurized hydraulic fluid, a hydraulic line system, including at least one line connecting the at least one hydraulic pump and the at least one hydraulic yaw motor, and at least one overpressure valve. The at least one overpressure valve is connected to a flow path of the hydraulic fluid between the at least one hydraulic pump and the at least one hydraulic motor.
In another aspect, a method of changing a yaw angle of a wind turbine nacelle is provided. The method includes providing a yaw drive system, which includes a hydraulic yaw motor for adjusting the yaw angle of a nacelle of a wind energy system, at least one hydraulic pump adapted for providing a pressurized hydraulic fluid, a hydraulic line system, including at least one line connecting the at least one hydraulic pump and the at least one hydraulic yaw motor, and at least one overpressure valve, wherein the at least one overpressure valve is connected to a flow path of the hydraulic fluid between the at least one hydraulic pump and the at least one hydraulic motor, and; actuating the at least one hydraulic yaw motor in order to change the yaw angle of the nacelle.
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.
The embodiments described herein include a wind turbine system that has a hydraulic yaw drive system with improved characteristics when subjected to high wind forces. More specifically, the yaw drive system is designed such that a valve in the hydraulic system may open during high loads caused by gusts, such that the nacelle may move, in response, or, as a result of the wind force, against the torque exerted by the yaw motor, or, in other words, the nacelle may “slip” due to the high load and thus passively react to the wind force.
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. As used herein, the term “yaw drive system” is intended to be representative of a system for the adjustment, respectively the manipulation of the yaw angle, of a nacelle of a wind turbine. As used herein, the term “overpressure valve” is intended to be representative of any device or system which is suitable to release pressure from a hydraulic system, if the pressure exceeds a predefined threshold. That is, an overpressure valve may be a mechanical overpressure valve, but may, for instance, also be a system able to sense a pressure with a sensor, and to control a release valve based on the information from the sensor signal.
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, 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 or yaw motor 244 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 continuous 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.
Between lines 212, 214 connecting the pump 210 and the motor 244, an overpressure valve 220 is located. The valve is typically adapted such that it does not affect, or only insignificantly affects, the flow of hydraulic fluid through lines 212, 214 from the pump to the motor. The valve is further adapted such that, if the pressure of the fluid in lines 212, 214 exceeds a certain predefined value, henceforth also called a threshold value, the valve opens and relieves the overpressure via line 222. The overpressure valve 220 is located in the flow path of the hydraulic fluid between the hydraulic pump and the hydraulic motor.
If, while hydraulic motor 244 is turning the nacelle 16, a strong gust of wind occurs which does not affect the rotor perpendicularly and symmetrically, the rotor 18 will exert a high torque on the nacelle 16 and will attempt to turn it. There are some load cases which produce particularly high torques in the yaw system. Firstly, a high load may be a reaction to an emergency stop of the wind turbine, particularly if the pitch angles of all blades are not reduced simultaneously. If the pitch angle of at least one of the rotor blades remains significantly larger than those of the other blades during the stopping procedure, a strong torque on the nacelle, and thus on the yaw drive system, may arise, which may be as high as five times the yaw drive torque during normal operating conditions. Further, a gust may act on only one side of the rotor, as gusts are a phenomenon typically limited to localized areas. In this case, one side of the rotor is affected by a significantly higher wind force, which also induces high loads in the yaw drive system. Such a torque affecting the nacelle ultimately results in a torque acting on motor 244, as the motor is, during the adjustment process, typically the only device preventing the nacelle 16 from rotating freely about its yaw axis 38. For better understanding, it is noted that all scenarios described to be problematic due to high loads relate to situations where the torque exerted by the wind on the nacelle is directed opposite to the torque exerted by the yaw drive system for turning the nacelle-rotor-system. The opposite case, wherein the wind-induced torque acts in the same direction as the motor torque, is typically non-critical, as the motor is then somewhat assisted by the wind-induced torque.
In the exemplary embodiment, the wind induced torque acts on motor 244 and thus leads to an increase of pressure in the hydraulic system. If the pressure reaches a predefined value, overpressure valve 220 opens and releases the pressure via line 222. As a result, the nacelle may move in a direction opposite to the direction in which it was previously moved by motor 244, hence the nacelle slips against the torque of the yaw motor. The nacelle may even turn, respectively slip, facilitated by the opened overpressure valve, about a considerable angle, e.g. up to 180° , against the torque exerted by the yaw motor. After the gust is over, the pressure in the hydraulic system decreases, and overpressure valve 220 closes. The motor 244 will thus continue to drive nacelle 16 in the original direction. The yaw drive system then, of course, has to firstly turn the nacelle back to the position before the slipping event, and then continues to turn the nacelle to the angular position which was the original objective of the adjustment process.
The wind force, above which the threshold pressure of valve 220 is typically reached, varies strongly between individual wind turbines. As a range of non-limiting examples, the overpressure valve 220 may be adapted to open if a horizontal gust of about 15 m/s to 25 m/s, more typically from 17 m/s to 23 m/s, acts on the wind turbine rotor at an angle of 45 degrees to the rotor's rotational axis during the yaw adjustment process.
There are at least two different cases of operation during gusts, which differ depending on the direction in which the gust exerts torque on the nacelle. The above described scenario applies if the torque exerted by a gust is opposite to the direction in which the motor 244 turns the nacelle. In other words, if the gust hinders the movement of the nacelle caused by the motor. This is the typical case in which the overpressure valve will open, as the motor has to work against the torque induced by the gust, which leads to increased pressure in lines 212, 214. In the other possible case, the gust turns the nacelle in the same direction in which the motor 244 is turning the nacelle. In this case, the reaction of the system depends strongly on the configuration of the hydraulic system and the types of pumps and motors used. In embodiments, an additional brake system is applied, such that the nacelle may be hindered from turning too fast if a gust acts in the same direction as the motor during a yaw adjustment process.
The threshold value or limit value for the pressure at which the overpressure valve opens is strongly dependent on the individual use case, in particular on the size of the wind turbine and on the particular type of hydraulic pump and motor system used. As a non-limiting example, if the hydraulic pump delivers hydraulic fluid at a standard pressure of 300 bar, the threshold value may be set to 330 bar to 500 bar, more typically from 350 bar to 450 bar. In other embodiments, the threshold value may be from 50 bar to 500 bar.
Both the hydraulic pump 210 and the hydraulic motor 244 may either be of a hydrodynamic or of a hydrostatic type. As non-limiting examples, the pump may be a gearpump, a radial piston pump or an axial piston pump, whereas the motor may be a gear and vane motor, an axial plunger motor or a radial piston motor. The advantages of different types of motors and pumps and how they may be combined with each other are well known to the skilled person.
Depending on the type of hydraulic motor chosen, the direction of movement of the motor is changed by an internal mechanism in the motor; in this case, only one pressure line from the pump to the motor is used, which is equipped with overpressure valve 220. Other types of motors require that there is one feed hydraulic feed line for each direction, and the direction of movement is dependent on the line which is used as a feed line. To select the direction of movement, a valve (not shown) is typically used to switch between either of the two lines. The embodiments described herein can be used with either type. For illustrational purposes, only one of the potentially two lines is shown in the figures, and the switching valve is not shown. In applications having two feed lines as described above, each feed line 212, 214 in the figures has to be considered to be representative of a double line, and in this case, each of the double lines has its own overpressure valve 220. Though, for illustrational purposes all embodiments depicted herein are shown with single lines from the hydraulic pump to the hydraulic motors, it shall be emphasized that all embodiments are also representative for embodiments with double feed lines, each of which is used for each direction of movement. Further, it shall be emphasized that in the depicted embodiments, the hydraulic motors include a mechanism for changing the direction of movement, and that these mechanisms are not shown for illustrational purposes. The skilled person will understand which standard measures and details are not shown in the figures for illustrational purposes, and will add them using his standard knowledge.
The above-described systems and methods facilitate yaw drive systems with reduced cost and size, which can replace or being used instead of conventional yaw drive systems with considerably larger size. Further, some embodiments of yaw drive systems described herein may support or replace conventional brake systems, such as disc brakes.
Exemplary embodiments of systems and methods for a yaw drive system for a wind turbine 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. Further, 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.
