Patent Application
20120025528
The invention relates to a magnetostrictive sensor system and method, and more particularly, to a magnetostrictive sensor system and method for use with wind turbines.
Wind turbines are well known. There are two basic types of commercial wind turbines, namely vertical axis wind turbines and horizontal axis wind turbines. Most horizontal axis wind turbines include a tower, a nacelle, a plurality of rotor blades, and a generator. The tower may be similar to electrical towers or it may be a steel tubular tower. The nacelle is a strong hollow shell that contains the inner workings of the wind turbine, including a low speed rotary shaft and a gearbox. It also includes the rotor blade pitch control and the yaw drive, which controls the position of the turbine relative to the wind. The nacelle also provides the anchor points for the rotor blades. The generator converts the harvested wind energy into electricity.
Wind turbines are subjected to several forms of force. Specifically, wind turbines can be subjected to linear forces as well as torsional forces. High winds and changing of direction for winds can create a load on wind turbines. Excessive loads on wind turbines can create damage to components of the turbines, for example cracking, or can lead to catastrophic failure.
A system and method for determining real-time forces being exerted on a wind turbine would be welcome in the art.
An embodiment of the invention includes a magnetostriction-based sensor system for sensing force on a wind turbine rotor shaft having multiple localized magnetized domains sensitive to magnetostriction. The magnetostriction-based sensor system includes at least two sets of first and second magnetometers, each set being located on one of the magnetized domains. Signals from the at least two sets of first and second magnetometers can be utilized to determine torsional and linear forces being exerted on the wind turbine rotor shaft.
In one aspect, the magnetostriction-based sensor system includes either a programmable logic controller (PLC) or the microcontroller that is configured to subtract signals of one of the first and second magnetometers from the other of the first and second magnetometers for each set of magnetometers to obtain a corrected magnetostrictive signal for each set of magnetometers.
In another aspect, the PLC or microcontroller is configured to add the corrected magnetostrictive signal of one set of magnetometers to the corrected magnetostrictive signal of another set of magnetometers located approximately 180 degrees around the rotor shaft to determine a real-time torsional force being exerted on the rotor shaft. The PLC or microcontroller is configured to subtract the corrected magnetostrictive signal of one set of magnetometers from the corrected magnetostrictive signal of another set of magnetometers located approximately 180 degrees around the rotor shaft to determine a real-time linear force being exerted on the rotor shaft.
An embodiment of the invention includes a wind turbine that includes a tower, a plurality of blades, and a nacelle positioned atop the tower and attached to the plurality of blades. The nacelle includes a low speed rotor shaft having a plurality of magnetized domains located about the rotor shaft and at least two sets of first and second magnetometers, each set being located on one of the magnetized domains, wherein signals from the at least two sets of first and second magnetometers can be utilized to determine real-time torsional and linear forces being exerted on the rotor shaft.
An embodiment of the invention includes a method of determining forces being exerted on a wind turbine rotor shaft. The method includes forming magnetized domains on a rotor shaft; providing pairs of first and second magnetometers, each pair being sited either on or offset from a respective magnetized domain on a rotor shaft; determining a magnetostrictive signal for each pair of first and second magnetometers; and determining from the magnetostrictive signals the force being exerted on the rotor shaft.
These and other features, aspects and advantages of the present invention may be further understood and/or illustrated when the following detailed description is considered along with the attached drawings.
The present specification provides certain definitions and methods to better define the embodiments and aspects of the invention and to guide those of ordinary skill in the art in the practice of its fabrication. Provision, or lack of provision, of a definition for a particular term or phrase is not meant to imply any particular importance, or lack thereof; rather, and unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art.
Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item, and the terms “front”, “back”, “bottom”, and/or “top”, unless otherwise noted, are merely used for convenience of description, and are not limited to any one position or spatial orientation. If ranges are disclosed, the endpoints of all ranges directed to the same component or property are inclusive and independently combinable.
The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described inventive features may be combined in any suitable manner in the various embodiments.
As illustrated in
A magnetostriction sensing system 140 includes two or more pairs of magnetostriction sensors, or magnetometers. The pairs of magnetometers are placed within each of the localized magnetized domains 135. As illustrated in
It should be appreciated that although the sensor positions have been illustrated and discussed as being sited at the localized magnetized domains 135, the sensor positions may instead be offset from the localized magnetized domains, either within the plane 137 or outside of the plane 137. Additionally, although the magnetostriction sensing system is shown to be in contact with the rotor shaft 104, it should be appreciated that non-contact sensing may be used instead. Although four sensor positions are illustrated, it should be understood that more or less than four sensor positions may be utilized. The number of sensor positions may correspond with the number of localized magnetized domains. It should be pointed out that the number of sensor positions should preferably be an even number, as signals from sensors at opposing sensor positions may be utilized in determining the force exerted on the wind turbine. Although a single plane 137 is illustrated, it should be understood that more than one plane 137 containing localized magnetized domains may be formed along the rotor shaft 104. Finally, it should be appreciated that additional sensors of, for example magnetic field and/or temperature, may be sited on the rotor shaft. Additional magnetometers may be used to monitor background magnetic fields, such as the earth's magnetic field and/or extraneous electro-magnetic interference (EMI), while additional temperature sensors may be used to monitor temperature changes. Temperature change and background magnetic interference can affect the signals from the primary magnetometers. By monitoring the temperature change and background magnetic interference, the magnitude of the effect can be mathematically eliminated by the microcontroller and/or the PLC.
The localized magnetization of certain regions of the rotor shaft 104 is accomplished in a way in which the regions remain magnetized for a lengthy period of time, preferably for the life of the rotor shaft. For example, the rotor shaft 104 may be subjected to a localized magnetization process as described in U.S. Pat. No. 7,631,564, the entire contents of which are incorporated herein by reference. As shown in
As illustrated, the magnetometers may be sited such that one magnetometer 142a is within the first region straddling the plane 137 and the second magnetometer 144a is within the second region straddling the plane 137. The benefit to siting the magnetometers thusly is to remove background field error and to double the magnetostrictive signal. In other words, both of the magnetometers are enabled to detect the same background magnetic field, but with an oppositely signed magnetostrictive signal. When subtracting these signals, the background field is removed but the magnetostrictive signal is doubled. Alternatively, the sensors 142a, 144a (and the other pairs of sensors) may be located offset from the localized magnetized domains 135.
In operation, the magnetometers at each sensor position measure a change in magnetic field strength of a specific localized magnetized domain. The measurements of each magnetostriction sensor at each sensor position are transmitted to either a microcontroller on the rotor shaft 104 or a programmable logic controller (PLC) located away from the rotor shaft. The microcontroller and/or the PLC are configured to subtract signals of one of the magnetometers from each sensor position from the other of the magnetometers from the same sensor position to obtain a corrected magnetostrictive signal for each set of magnetometers.
Then, having obtained corrected magnetostrictive signals for each sensor position, the microcontroller and/or the PLC are configured to add the corrected magnetostrictive signal from the set of magnetometers at one sensor position to the corrected magnetostrictive signal of another set of magnetometers located at a sensor position approximately 180 degrees around the rotor shaft to determine a real-time torsional force being exerted on the rotor shaft. Further, the microcontroller and/or the PLC are configured to subtract the corrected magnetostrictive signal from the set of magnetometers at one sensor position from the corrected magnetostrictive signal of another set of magnetometers located at a sensor position approximately 180 degrees around the rotor shaft to determine a real-time linear force being exerted on the rotor shaft. In this way, the magnetometers, in combination with the microcontroller and/or PLC, can determine in real-time both linear and torsional forces being exerted on the rotor shaft 104.
Some wind turbines include a flange at one end thereof, as well as bearings and labyrinth seals positioned about the rotor shaft. The magnetostriction sensing system 140 may be sited in one or more sections of the rotor shaft. For example, the magnetostriction sensing system 140 may be sited between the flange and the bearings. Alternatively, the magnetostriction sensing system 140 may be sited on the far side of the bearings from the flange. For larger turbines, such as 3.5 megawatt turbines that include a pair of bearings, the magnetostriction sensing system 140 may be sited before the flange; after flange but before the first bearings; between the bearings; or after the second bearings. Magnetometers can be located immediately after the bearings or within a certain distance after. Proper siting of the siting of the magnetostriction sensing system should be where the forces affecting the rotor shaft are at their highest so that the greatest signals can be obtained there.
Option B includes a wireless power supply 176, a wireless data transfer apparatus 178, and data storage on a programmable logic controller 180. In one embodiment, the wireless power supply 176 is an inductive power supply. The wireless power supply 176, the wireless data transfer apparatus 178, and the programmable logic controller 180 are located apart from the rotor shaft 104.
It should be appreciated that, for Options B and C, a redundant battery, such as battery 172, can be included in the system. The redundant battery would run the system during a power failure and shutdown of the turbine. During normal operation, the battery would be in a stand-by mode.
It should be appreciated that the collected data from the sensing signals can be used as an input for active control of various factors related to the wind turbine. Some of the factors can be pitch drive and yaw angle for example. Another factor is active braking, which is based on controlling the active power intake of the power converters. Specifically, the sensing signals can be used to reduce loads and to reduce component fatigue on various turbine parts, such as shafts, gearbox, bearings, blades, and the tower itself, for example. The sensing signals can be used to adjust the blade angles, the yaw angle, and converter output power, either during operation or during emergency stops.
Data transferred to the controller 170 is further transferred to the wireless data transfer apparatus 178 through a single ended data transfer element, such as a RS232. Specifically, in the communication loop between the controller 170 and the data transfer apparatus 178, the controller 170 is, for example, a slave or producer in a RS232 standard-based communication protocol. The programmable logic controller acts as a master, or as a consumer, in this configuration. Between these two fundamental entities, wireless modules and protocol/standard adapters can be implemented. Bluetooth and Wi-Fi are examples of suitable wireless standards that can be utilized. It should be appreciated that, as mentioned before, other protocols, architectures, or standards can be used.
The configuration of
It further should be appreciated that analog filtering is but one example of a suitable electronics configuration. For example, digital notch-filtering and switched capacitor based filtering can be utilized instead of analog filtering.
In one embodiment, a complete sensor system includes sixteen magnetometers, eight of which are used for redundancy and to detect background magnetic field strength. Additionally, temperature sensors are applied to the rotor shaft 104 to measure temperature fluctuations that will be used to compensate out the environmental changes. The read-out electronics will include amplification, analog filtering, temperature compensation, and analog-to-digital conversion (ADC). The read-out electronics can be mounted on a flexible printed circuit board (PCB), which is better suited for mounting onto cylindrical shafts. The ADC is performed in the vicinity of the sensors to minimize the effects of electromagnetic interference (EMI). Any EMI can be suppressed through Mu-metal shielding, the use of digital signal transmission, and analog paths that are short, on the order of about 10 millimeters. Mu-metal shielding is shielding including particular metals that having properties that make it very efficient to shield magnetic fields from coupling to electrical circuits. Examples of suitable mu-metals include a nickel-iron alloy (approximately 75% nickel, 15% iron, plus copper and molybdenum) that has very high magnetic permeability.
Other sensors, such as, for example, background magnetic field sensors and temperature sensors, may be included within the sensor system an used to correct for background magnetic field and/or temperature effects on the magnetostriction signals. Additionally, there are some instances when a wind turbine is not coincident with the earth's gravitation vector. In such instances, a small error may occur when the nacelle rotates. Some magnetic field or position sensors may be included to measure yaw angle to so that the yaw angle error may be corrected for.
The embodiments of the invention described herein will enable greater control of asymmetrical loads on wind turbines. By being more able to determine asymmetrical loads on a wind turbine, the operating parameter margins for wind turbines can be decreased, allowing wind turbine operators the ability to get greater power out of the wind turbines.
The embodiments of the invention can be used to measure time-domain signals or to perform frequency transform for the purpose of monitoring any natural and unwanted oscillation modes of a turbine. Further, signals generated by embodiments of the invention can be used to actively control yaw angle, blade pitch angles, and braking power due to the converter intake, for example.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, while embodiments have been described in terms that may initially connote singularity, it should be appreciated that multiple components may be utilized. Further, while the magnetometer positions have been shown and described on low speed rotor shafts, it should be understood that such magnetometers can be sited on any suitable high strength steel structure having magnetostrictive properties, such as, for example, high speed shafts, bearings, gearbox, and possibly the tower if fabricated out of appropriate material. Also, while the wind turbines that have been illustrated and described include a gearbox and a high-speed shaft, it should be appreciated that other forms of wind turbines can be utilized with the magnetometers. For example, direct drive systems, can be used in commercial wind turbines. In direct drive systems, the gearbox and high-speed shaft is omitted. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
