Patent Description:
Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a nacelle fixed atop a tower, a generator and a gearbox housed with the nacelle, and a rotor configured with the nacelle having a rotatable hub with one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

The rotor blades generally include a suction side shell and a pressure side shell secured together at bond lines along the leading and trailing edges of the blade. Further, the pressure and suction shells are relatively lightweight and have structural properties (e.g., stiffness, buckling resistance and strength) which are not configured to withstand the bending moments and other loads exerted on the rotor blade during operation. Thus, to increase the stiffness, buckling resistance, and strength of the rotor blade, the body shell is typically reinforced using one or more structural components (e.g. opposing spar caps with a shear web configured therebetween) that engage the inner pressure and suction side surfaces of the shell halves. The spar caps and/or shear web may be constructed of various materials, including but not limited to glass fiber laminate composites and/or carbon fiber laminate composites. <CIT> relates to a horizontal axis wind turbine, wherein when a wind speed is above a predetermined value, a yaw angle of the nacelle is fixed, a pitch angle of the blade is controlled in accordance with a yaw angle of the wind direction relative to the nacelle. <CIT> relates to a wind turbine.

In recent years, wind turbines for wind power generation have increased in size to achieve improvement in power generation efficiency and to increase the amount of power generation. Along with the increase in size of wind turbines for wind power generation, wind turbine rotor blades have also increased in size. With this increased size, the wind turbine structure as well as the rotor blades can also experience increased loading.

For example, high wind speed zones (e.g. hurricanes, typhoons, etc.) create challenges for large wind turbines, where the risk to the structure becomes very high, particularly when the wind turbine does not have any structural reinforcement. One such risk is flutter phenomenon, which generally refers to the dynamic instability of an elastic structure in a fluid flow, caused by positive feedback between the body's deflection and the force exerted by the fluid flow.

Thus, to minimize the negative effects mentioned herein, it would be advantageous for the wind turbine to include a control logic that protects wind turbines from flutter during high wind speeds. Accordingly, the present disclosure is directed to improved systems and methods that reduce or eliminate flutter by modifying blade pitch angle of the wind turbine.

In one aspect, the present disclosure is directed to a method for protecting an idling wind turbine power system from damage during loss of grid power according to independent claim <NUM>. A wind turbine power system has a plurality of rotor blades. A method includes monitoring an incoming wind direction at the wind turbine power system. When the incoming wind direction is changing at a predetermined attack angle, the method also includes rotating at least one of the rotor blades of the wind turbine power system to a pitch angle that is offset from a feather position by a predetermined number of degrees to reduce and/or eliminate flutter phenomenon from occurring.

In one embodiment, the method may also include determining at least one of a rotor position or a rotor orientation of the wind turbine power system and rotating at least one of the rotor blades of the wind turbine power system to the pitch angle that is offset from the feather position by the predetermined number of degrees when the rotor position and/or the rotor orientation are indicative of the flutter phenomenon occurring.

The method further includes yawing the nacelle of the wind turbine approximately <NUM> degrees away from the incoming wind direction when the incoming wind direction is changing at the predetermined attack angle. The predetermined number of degrees includes less than about <NUM> degrees.

In additional embodiments, rotating at least one of the rotor blades to the pitch angle that is offset from a feather position by the predetermined number of degrees may include rotating each of the plurality of rotor blades by the same number of degrees. In alternative embodiments, rotating at least one of the rotor blades to the pitch angle that is offset from a feather position by the predetermined number of degrees may include rotating each of the plurality of rotor blades by a different number of degrees.

In particular embodiments, the feather position may include a position in which a chord of the rotor blade is approximately inline with the incoming wind direction at stand still or minimal rotation.

The method includes utilizing backup energy stored in the wind turbine power system for powering one or more wind turbine components during the loss of grid power, the one or more wind turbine components comprising one or more yaw drive mechanisms. The wind turbine power system includes at least one energy storage device for storing the backup energy. In addition, the wind turbine component(s) may include one or more pitch drive mechanisms, a brake, a main controller, and/or one or more electrical components of the wind turbine power system.

In further embodiments, if the main controller of the wind turbine power system is offline due to the loss of grid power, the energy storage device is configured to power operation of the wind turbine power system without interruption.

In another aspect, the present disclosure is directed to a backup control system for protecting an idling wind turbine power system from damage during loss of grid power according to the independent system claim. A backup control system includes a pitch control system having an auxiliary power supply and a plurality of pitch drive mechanisms communicatively coupled to the auxiliary power supply via a communication link. As such, during the loss of grid power, the auxiliary power supply powers the pitch control system to implement a control scheme for the wind turbine power system. The control scheme includes monitoring an incoming wind direction at the wind turbine power system. When the incoming wind direction is changing at a predetermined attack angle, the control scheme includes rotating at least one of the plurality of rotor blades of the wind turbine power system to a pitch angle that is offset from a feather position by a predetermined number of degrees to reduce and/or eliminate flutter phenomenon from occurring. It should be understood that the method may also include any of the steps and/or features as described herein.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> according to the present disclosure. As shown, the wind turbine <NUM> generally includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator <NUM> (<FIG>) positioned within the nacelle <NUM> to permit electrical energy to be produced.

The wind turbine <NUM> may also include a wind turbine controller <NUM> centralized within the nacelle <NUM>. For example, as shown, the turbine controller <NUM> is located in the top box cabinet <NUM> (<FIG>). However, in other embodiments, the controller <NUM> may be located within any other component of the wind turbine <NUM> or at a location outside the wind turbine <NUM>. Further, the controller <NUM> may be communicatively coupled to any number of the components of the wind turbine <NUM> in order to control the operation of such components and/or implement a correction action. As such, the controller <NUM> may include a computer or other suitable processing unit. Thus, in several embodiments, the controller <NUM> may include suitable computer-readable instructions that, when implemented, configure the controller <NUM> to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. Accordingly, the controller <NUM> may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences), de-rating or up-rating the wind turbine, and/or individual components of the wind turbine <NUM>.

Referring now to <FIG>, a simplified, internal view of one embodiment of the nacelle <NUM> of the wind turbine <NUM> shown in <FIG> is illustrated. As shown, a generator <NUM> may be disposed within the nacelle <NUM>. In general, the generator <NUM> may be coupled to the rotor <NUM> for producing electrical power from the rotational energy generated by the rotor <NUM>. For example, as shown in the illustrated embodiment, the rotor <NUM> may include a rotor shaft <NUM> coupled to the hub <NUM> for rotation therewith. The rotor shaft <NUM> may, in turn, be rotatably coupled to a generator shaft <NUM> of the generator <NUM> through a gearbox <NUM>. As is generally understood, the rotor shaft <NUM> may provide a low speed, high torque input to the gearbox <NUM> in response to rotation of the rotor blades <NUM> and the hub <NUM>. The gearbox <NUM> may then be configured to convert the low speed, high torque input to a high speed, low torque output to drive the generator shaft <NUM> and, thus, the generator <NUM>.

The wind turbine <NUM> may also a yaw drive mechanism <NUM> configured to change the angle of the nacelle <NUM> relative to the wind (e.g., by engaging a yaw bearing <NUM> of the wind turbine <NUM> that is arranged between the nacelle <NUM> and the tower <NUM> of the wind turbine <NUM>). Further, each yaw drive mechanism <NUM> may include a yaw drive motor <NUM> (e.g., any suitable electric motor), a yaw drive gearbox <NUM>, and a yaw drive pinion <NUM>. In such embodiments, the yaw drive motor <NUM> may be coupled to the yaw drive gearbox <NUM> so that the yaw drive motor <NUM> imparts mechanical force to the yaw drive gearbox <NUM>. Similarly, the yaw drive gearbox <NUM> may be coupled to the yaw drive pinion <NUM> for rotation therewith. The yaw drive pinion <NUM> may, in turn, be in rotational engagement with the yaw bearing <NUM> coupled between the tower <NUM> and the nacelle <NUM> such that rotation of the yaw drive pinion <NUM> causes rotation of the yaw bearing <NUM>. Thus, in such embodiments, rotation of the yaw drive motor <NUM> drives the yaw drive gearbox <NUM> and the yaw drive pinion <NUM>, thereby rotating the yaw bearing <NUM> and the nacelle <NUM> about the yaw axis <NUM>. Similarly, the wind turbine <NUM> may include pitch control system <NUM> having one or more pitch adjustment mechanisms <NUM> communicatively coupled to the wind turbine controller <NUM>, with each pitch adjustment mechanism(s) <NUM> being configured to rotate the pitch bearing <NUM> and thus the individual rotor blade(s) <NUM> about the pitch axis <NUM>.

In addition, the wind turbine <NUM> may also include one or more sensors <NUM> for monitoring various wind conditions of the wind turbine <NUM>. For example, the incoming wind direction <NUM>, wind speed, or any other suitable wind condition near of the wind turbine <NUM> may be measured, such as through use of a suitable weather sensor <NUM>. Suitable weather sensors <NUM> include, for example, Light Detection and Ranging ("LIDAR") devices, Sonic Detection and Ranging ("SODAR") devices, anemometers, wind vanes, barometers, radar devices (such as Doppler radar devices) or any other sensing device which can provide wind directional information now known or later developed in the art.

Referring now to <FIG>, a block diagram of one embodiment of the controller <NUM> according to the present disclosure is illustrated. As shown, the controller <NUM> may include a computer or other suitable processing unit that may include suitable computer-readable instructions that, when implemented, configure the controller <NUM> to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. More specifically, as shown, there is illustrated a block diagram of one embodiment of suitable components that may be included within the controller <NUM> in accordance with example aspects of the present disclosure. As shown, the controller <NUM> may include one or more processor(s) <NUM> and associated memory device(s) <NUM> configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like disclosed herein).

As used herein, the term "processor" refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) <NUM> may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements.

Such memory device(s) <NUM> may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) <NUM>, configure the controller <NUM> to perform various functions as described herein. Additionally, the controller <NUM> may also include a communications interface <NUM> to facilitate communications between the controller <NUM> and the various components of the wind turbine <NUM>. An interface can include one or more circuits, terminals, pins, contacts, conductors, or other components for sending and receiving control signals. Moreover, the controller <NUM> may include a sensor interface <NUM> (e.g., one or more analog-to-digital converters) to permit signals transmitted from the sensors to be converted into signals that can be understood and processed by the processors <NUM>.

Referring now to <FIG>, a distributed control system <NUM> for a wind turbine, such as wind turbine <NUM> of <FIG>, according to one embodiment of the disclosure is illustrated. As shown, the control system <NUM> may include the main wind turbine controller <NUM> and a plurality of distributed input and output (I/O) modules <NUM>, <NUM>, <NUM> for individual control of one or more wind turbine components. Thus, as will be described herein, the distributed control system <NUM> has backup capabilities for protecting the system <NUM> from damage during loss of grid power.

More specifically, as shown in the illustrated embodiment, the control system <NUM> includes a top box distributed I/O module <NUM>, a downtower distributed I/O module <NUM>, and a tower distributed I/O module <NUM>. Further, as shown, each of the distributed I/O modules <NUM>, <NUM>, <NUM> are connected to the main turbine controller <NUM> via a plurality of communication link <NUM> for command and monitoring. It should be understood that the communications links <NUM> as described herein may include any suitable communication medium for transmitting the signals. For instance, the communications links <NUM> may include any number of wired or wireless links, including communication via one or more Ethernet connections, fiber optic connections, network buses, power lines, conductors, or circuits for transmitting information wirelessly. Further, signals may be communicated over the communications links <NUM> using any suitable communication protocol, such as a serial communication protocol, broadband over power line protocol, wireless communication protocol, or other suitable protocol.

Thus, during normal operation, the turbine controller <NUM> is configured to receive information from the input modules and send information to output modules. The inputs and outputs can be either analog signals which are continuously changing or discrete signals. More specifically, in certain embodiments, the top box distributed I/O module <NUM> is configured to provide I/O to the turbine controller <NUM> so as to control uptower components of the wind turbine <NUM>, e.g. the yaw drive mechanisms <NUM> and/or the pitch drive mechanisms <NUM>. Similarly, the downtower distributed I/O module <NUM> is configured to provide I/O to the turbine controller <NUM> so as to control the downtower electrical assembly, e.g. transformers, etc. The tower distributed I/O module <NUM> is configured to provide I/O to the tower components as described herein. In addition, the control system <NUM> may include more or less distributed I/O modules than those depicted in <FIG> depending on the specific components of the wind turbine <NUM>.

Referring still to <FIG>, the control system <NUM> of the present disclosure includes a yaw system <NUM> having a plurality of yaw system components configured to change an angle of the nacelle <NUM> of the wind turbine <NUM> relative to the incoming wind direction <NUM> that can operate through various failures of the overall system <NUM>. In addition, as shown, the control system <NUM> may include an auxiliary power supply <NUM> having a hydraulic brake power control device (e.g. a variable frequency drive <NUM>). As such, the auxiliary power supply <NUM> is configured to power all programmable logic controllers (PLC) of the control system <NUM>, as well as providing the communication and controls of the control system <NUM>. In addition, the control system <NUM> may include a filter unit <NUM> that is connected to the output of the auxiliary power supply <NUM>. For example, in one embodiment, the auxiliary power supply <NUM> may correspond to a fixed frequency inverter (i.e. running at desired frequency that is equal to the prevailing grid frequency) that provides a PWM output. In such an embodiment, the filter unit <NUM> may include a sinusoidal filter to eliminate the harmonics of the output.

The control system <NUM> may further include a braking unit <NUM> coupled to the variable frequency drive <NUM>. More specifically, as shown in the illustrated embodiment, the braking unit <NUM> may include a brake chopper <NUM> coupled to the variable frequency drive <NUM> and at least two dynamic brake resistors <NUM>, <NUM> coupled to the brake chopper <NUM>. As such, the multiple dynamic brake resistors <NUM>, <NUM> provide redundancy to the braking unit <NUM> in the event of a resistor failure.

Further, as shown, the control system <NUM> includes at least two energy storage devices <NUM>, <NUM> coupled to the braking unit <NUM>. More specifically, as shown, each of the energy storage device(s) <NUM>, <NUM> may include at least two battery units <NUM>, <NUM> coupled to at least two battery chargers <NUM>, <NUM> via a fuse <NUM>. In other words, the battery units <NUM>, <NUM> and/or battery chargers <NUM>, <NUM> are designed to operate in a load-sharing configuration, with each of the battery units <NUM>, <NUM> and/or battery chargers <NUM>, <NUM> capable of taking the complete load. Further, the fuse <NUM> described herein provides DC fuse protection at the output of battery unit(s) <NUM>, <NUM>, particularly for overload and arc flash protection against short circuits.

As mentioned, the control system <NUM> also includes the yaw drive mechanisms <NUM> (including, at least, the yaw drive motor <NUM> and the yaw bearing <NUM>) and the pitch drive mechanisms <NUM> described herein that are communicatively coupled to the auxiliary power supply <NUM> and the main controller <NUM> via one or more communication links <NUM>. More specifically, as shown, each of the yaw drive mechanisms <NUM> includes a yaw power control device (e.g. yaw variable frequency drive <NUM>). For example, in certain embodiments, the yaw variable frequency drives <NUM> may correspond to four-quad front end converters that provide back-to-back AC DC bridges to enable energy flow in both the directions with a common DC bus. In addition, as shown, the control system <NUM> may include a multiple-winding transformer <NUM> to facilitate the bidirectional energy transfer, thereby enabling the exchange of energy between all system components.

Referring still to <FIG>, the yaw system <NUM> may also include one or more controllers <NUM> configured to control the variable frequency drives <NUM>. For example, in one embodiment, the yaw variable frequency drives <NUM> may correspond to intelligent converters each having a separate controller <NUM> configured to evaluate the forces locally and compare with one or more driving command(s), which eliminates the dependency on the turbine controller <NUM>. In addition, as shown, the pitch control system <NUM> may also be connected to the auxiliary power supply <NUM> via a communication link <NUM>. In addition, as mentioned, the pitch control system <NUM> may include the pitch drive mechanisms <NUM> (i.e. one for each rotor blade <NUM>). Thus, during the loss of grid power, the auxiliary power supply <NUM> powers the pitch control system <NUM> to implement a control scheme for the wind turbine power system <NUM>.

Referring now to <FIG>, a flow chart <NUM> of a method for protecting a wind turbine power system from damage during loss of grid power according to the present disclosure is illustrated. In general, the method <NUM> will be described herein with reference to the wind turbine <NUM> and control system <NUM> shown in <FIG>. However, it should be appreciated that the disclosed method <NUM> may be implemented with rotor blades having any other suitable configurations. In addition, although <FIG> depicts steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and/or adapted in various ways without deviating from the scope of the present disclosure.

As shown at (<NUM>), the method <NUM> may include monitoring an incoming wind direction at the wind turbine power system <NUM>. As shown at (<NUM>), the method <NUM> includes determining whether the wind direction is changing at a predetermined attack angle. If so, as shown at (<NUM>), the method <NUM> may include implementing a control scheme <NUM> for the wind turbine power system <NUM>. For example, as shown at (<NUM>), the control scheme <NUM> may include rotating at least one of the rotor blades <NUM> to a pitch angle that is offset from a feather position by a predetermined number of degrees to reduce and/or eliminate flutter phenomenon from occurring. In such embodiments, the feather position described herein may include a position in which a chord of the rotor blade <NUM> is approximately inline with the incoming wind direction <NUM> at stand still or minimal rotation.

In one embodiment, as shown at (<NUM>), the control scheme <NUM> may also include determining a rotor position and/or a rotor orientation of the wind turbine power system <NUM> and rotating at least one of the rotor blades <NUM> to the pitch angle that is offset from the feather position by the predetermined number of degrees when the rotor position and/or the rotor orientation are indicative of the flutter phenomenon occurring. More specifically, in one embodiment, the predetermined number of degrees is less than about <NUM> degrees, such as less than about <NUM> degrees. In such embodiments, the minuscule deviation/offset of individual blades <NUM> from the feather position is configured to result in drastic reductions in flutter and is possible due to the control system <NUM> having significant stored backup energy that is available during loss of grid power. In certain embodiments, the method <NUM> may include rotating each of the rotor blades <NUM> away from the feather position by the same number of degrees. In alternative embodiments, the method <NUM> may include rotating each of the rotor blades <NUM> away from the feather position by a different number of degrees.

The method <NUM> further includes yawing the nacelle <NUM> approximately <NUM> degrees away from the incoming wind direction <NUM> when the incoming wind direction <NUM> is changing at the predetermined attack angle.

The method <NUM> also includes utilizing backup energy stored in the wind turbine power system <NUM> for powering one or more wind turbine components during the loss of grid power. One or more of the energy storage devices <NUM>, <NUM> are configured for storing the backup energy. As such, if the main controller <NUM> of the wind turbine power system <NUM> is offline due to the loss of grid power, the energy storage devices <NUM>, <NUM> are configured to power operation of the wind turbine power system <NUM> without interruption.

Claim 1:
A method (<NUM>) for protecting an idling wind turbine power system (<NUM>) from damage during loss of grid power, the wind turbine power system (<NUM>) having a plurality of rotor blades (<NUM>), the method (<NUM>) comprising:
monitoring an incoming wind direction (<NUM>) at the wind turbine power system (<NUM>);
when the incoming wind direction (<NUM>) is changing at a predetermined attack angle, rotating at least one of the plurality of rotor blades (<NUM>) of the wind turbine power system (<NUM>) to a pitch angle that is offset from a feather position by a predetermined number of degrees to reduce and/or eliminate flutter phenomenon from occurring, wherein the predetermined number of degrees comprises less than about <NUM> degrees;
utilizing backup energy stored in the wind turbine power system (<NUM>) for powering one or more wind turbine (<NUM>) components during the loss of grid power, wherein the wind turbine power system (<NUM>) further comprises at least one energy storage device for storing the backup energy, and wherein the one or more wind turbine (<NUM>) components comprises one or more yaw drive mechanisms; and
yawing the nacelle of the wind turbine (<NUM>) approximately <NUM> degrees away from the incoming wind direction (<NUM>) when the incoming wind direction (<NUM>) is changing at the predetermined attack angle.