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 modern wind turbine typically includes a tower, a nacelle rotatably supported on the tower, a generator housed in the nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles, and transmit the kinetic energy through rotational energy to turn a shaft that couples 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. With the growing interest in wind generated electricity, considerable efforts have been made to develop wind turbines that are reliable and efficient.

Current wind turbines typically include an overspeed monitoring system that monitors the rotor speed relative to a fixed overspeed setting(s) (i.e., a fixed maximum rotor speed setting(s) for the wind turbine). In general, the fixed overspeed setting(s) is determined as a function of the predetermined, nominal speed for the wind turbine. For example, the fixed overspeed setting(s) may be set as a maximum speed setting that is greater than the wind turbine's nominal speed. In such instance, if the rotor speed for the wind turbine exceeds the fixed overspeed setting(s), a control action may be implemented by the overspeed monitoring system to reduce the rotor speed and/or to shutdown the wind turbine. <CIT> relates to a method for controlling a wind turbine generator.

In many instances, it is desired to operate a wind turbine at reduced speeds (e.g., at a speed setting below the turbine's nominal speed). For example, a wind turbine may often be operated at a derated speed to compensate for the higher loads caused by higher air densities. Unfortunately, given the configuration of conventional overspeed monitoring systems, the fixed overspeed setting(s) applied by a current monitoring system is the same regardless of whether the speed setpoint for the wind turbine is set at the nominal speed or a reduced speed. Thus, if a failure of the turbine controller occurs while the wind turbine is operating at reduced speeds, the turbine rotor is allowed to accelerate across a large range of speed values from the reduced rotor speed to the fixed overspeed setting(s) prior to any control action being implemented by the overspeed monitoring system. Such significant acceleration of the rotor often results in the load capabilities of one or more of the wind turbine components being exceeded, thereby leading to damage and/or failure of such component(s).

Accordingly, a system and method for improved overspeed monitoring of a wind turbine operating at reduced rotor speeds (e.g., at a speed setpoint below its nominal speed) would be welcomed in the technology.

In one aspect, the present subject matter is directed to a method for overspeed monitoring of a wind turbine according to claim <NUM>. The method generally includes monitoring, with a control device, an actual rotor speed of the wind turbine while the wind turbine is operating at a current speed setpoint and referencing, with the control device, a dynamic overspeed setting for the wind turbine. The method also includes determining, with the control device, a final overspeed setting to be applied for the wind turbine based on a comparison between the dynamic overspeed setting and a predetermined overspeed setting for the wind turbine, wherein determining the final overspeed setting for the wind turbine includes selecting the final overspeed setting as a minimum of the dynamic overspeed setting and the predetermined overspeed setting. The method includes comparing, with the control device, the actual rotor speed of the wind turbine to the final overspeed setting, and when the actual rotor speed is equal to or exceeds the final overspeed setting, initiating, with the control device, a control action to adjust an operation of the wind turbine in a manner that reduces the actual rotor speed.

In another aspect, the present subject matter is directed to an overspeed monitoring system for a wind turbine according to the independent system claim. The system includes a turbine controller configured to control one or more components of the wind turbine so that the wind turbine operates at a current speed setpoint. The turbine controller is also configured to determine a dynamic overspeed setting for the wind turbine. The system also includes an overspeed control device communicatively coupled to the turbine controller. The overspeed control device is configured to receive the dynamic overspeed setting from the turbine controller and determine a final overspeed setting to be applied for the wind turbine based on a comparison between the dynamic overspeed setting and a predetermined overspeed setting for the wind turbine, wherein determining the final overspeed setting for the wind turbine includes selecting the final overspeed setting as a minimum of the dynamic overspeed setting and the predetermined overspeed setting. The overspeed control device is also configured to monitor an actual rotor speed of the wind turbine and compare the actual rotor speed to the final overspeed setting. In addition, when the actual rotor speed is equal to or exceeds the final overspeed setting, the control device is configured to initiate a control action to adjust the operation of the wind turbine in a manner that reduces the actual rotor speed.

In general, the present subject matter is directed to a system and method for overspeed monitoring of a wind turbine. In particular, the disclosed system and method provided from improved overspeed monitoring when a wind turbine is operating at reduced or derated rotor speeds (i.e., at a speed setpoint below the nominal speed for the wind turbine). As will be described below, in several embodiments, a turbine controller of the wind turbine may be configured to calculate a dynamic overspeed setting that varies as a function of a current speed-related parameter of the wind turbine, such as the current speed setpoint for the wind turbine or the current air density of the air surrounding the wind turbine. The calculated dynamic overspeed setting may then be transmitted to an independent overspeed control device of the wind turbine. The overspeed control device also includes a fixed overspeed setting stored therein that is determined as a function of the nominal speed for the wind turbine. Upon receipt of the dynamic overspeed setting, the overspeed control device may determine the overspeed setting to be applied for the wind turbine by selecting the minimum overspeed setting between the dynamic overspeed setting and the fixed overspeed setting. Given that the dynamic overspeed setting is determined as a function of a current speed-related parameter for the wind turbine as opposed to its fixed nominal speed, the dynamic overspeed setting may be less than the fixed overspeed setting when the wind turbine is operating at reduced rotor speeds. As such, the overspeed control device may utilize the reduced, dynamic overspeed setting to monitor the rotor speed in a manner that can prevent the occurrence of extreme loading conditions in the event of a controller failure for a speed-derated wind turbine.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> in accordance with aspects of the present subject matter. 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 turbine control system or turbine controller <NUM> centralized within the nacelle <NUM> (or disposed at any other suitable location within and/or relative to the wind turbine <NUM>). In general, the turbine controller <NUM> may comprise a computing device or any other suitable processor-based device. Thus, in several embodiments, the turbine 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. As such, the turbine controller <NUM> may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences) and/or components of the wind turbine <NUM>. For example, the controller <NUM> may be configured to adjust the blade pitch or pitch angle of each rotor blade <NUM> (i.e., an angle that determines a perspective of the blade <NUM> with respect to the direction of the wind) about its pitch axis <NUM> in order to control the rotational speed of the rotor blade <NUM> and/or the power output generated by the wind turbine <NUM>. For instance, the turbine controller <NUM> may control the pitch angle of the rotor blades <NUM>, either individually or simultaneously, by transmitting suitable control signals to one or more pitch drives or pitch adjustment mechanisms <NUM> (<FIG>) of the wind turbine <NUM>. Similarly, the turbine controller <NUM> may be configured to adjust the yaw angle of the nacelle <NUM> (i.e., an angle that determines a perspective of the nacelle <NUM> relative to the direction of the wind) about a yaw axis (not shown) of the wind turbine <NUM>. For example, the controller <NUM> may transmit suitable control signals to one or more yaw drive mechanisms <NUM> (<FIG>) of the wind turbine <NUM> to automatically control the yaw angle.

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 in accordance with aspects of the present subject matter. 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>.

Additionally, as indicated above, the controller <NUM> may also be located within the nacelle <NUM> (e.g., within a control box or panel). 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>. As is generally understood, 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. For example, as indicated above, the controller <NUM> may be communicatively coupled to each pitch adjustment mechanism <NUM> of the wind turbine <NUM> (one for each rotor blade <NUM>) via a pitch controller <NUM> to facilitate rotation of each rotor blade <NUM> about its pitch axis <NUM>. Similarly, the controller <NUM> may be communicatively coupled to one or more yaw drive mechanisms <NUM> of the wind turbine <NUM> for adjusting the yaw angle or position of the nacelle <NUM>. For instance, the yaw drive mechanism(s) <NUM> may be configured to adjust the yaw position by rotationally engaging a suitable yaw bearing <NUM> (also referred to as a slewring or tower ring gear) of the wind turbine <NUM>, thereby allowing the nacelle <NUM> to be rotated about its yaw axis.

It should be appreciated that the turbine controller <NUM> may, in several embodiments, correspond to a processor-based device, such as a computing device or any combination of computing devices. For example, the turbine controller <NUM> may generally include one or more processor(s) and associated memory 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) 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 may generally be configured to store information accessible to the processor(s), including data that can be retrieved, manipulated, created and/or stored by the processor(s) and instructions that can be executed by the processor(s). For instance, the memory device(s) may be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the turbine controller <NUM> to perform various computer-implemented functions including, but not limited to, any of the control functions described herein. It should also be appreciated that the turbine controller <NUM> may include any suitable hardware that allows the controller <NUM> to function as described herein. For instance, the instructions or logic for the controller <NUM> may, in one embodiment, be implemented by hard-wired logic or other circuitry.

In addition, the wind turbine <NUM> may also include one or more sensors for monitoring various operating parameters of the wind turbine <NUM>. For example, in several embodiments, the wind turbine <NUM> may include one or more speed sensors <NUM> configured to monitor one or more speed-related operating parameters of the wind turbine <NUM>, such as the current rotor speed of the wind turbine <NUM>, the current generator speed of the wind turbine <NUM> and/or the current air density of the air surrounding the wind turbine <NUM>. Of course, the wind turbine <NUM> may further include various other suitable sensors for monitoring any other suitable operating conditions of the wind turbine <NUM>.

It should be appreciated that the various sensors described herein may correspond to pre-existing sensors of a wind turbine <NUM> and/or sensors that have been specifically installed within the wind turbine <NUM> to allow one or more operating parameters to be monitored. It should also be appreciated that, as used herein, the term "monitor" and variations thereof indicates that the various sensors of the wind turbine <NUM> may be configured to provide a direct measurement of the operating parameters being monitored or an indirect measurement of such operating parameters. Thus, the sensors may, for example, be used to generate signals relating to the operating parameter being monitored, which can then be utilized by the controller <NUM> to determine the actual operating parameters.

As shown in <FIG>, the wind turbine may also include an independent overspeed control device <NUM> configured to monitor the rotor speed of the wind turbine <NUM> so as to determine when the rotor speed reaches or exceeds a given overspeed setting(s) (e.g., a maximum speed limit) for the wind turbine <NUM>. In several embodiments, the overspeed control device may correspond to a separate device from the turbine controller <NUM> (e.g., as shown in <FIG>). Thus, the overspeed control device <NUM> may monitor the rotor speed independently from the turbine controller <NUM>, which may allow the overspeed control device <NUM> to implement or initiate a corrective or control action to adjust the operation of the wind turbine when an overspeed condition is detected for the wind turbine <NUM> regardless of whether the turbine controller <NUM> is functioning properly. Accordingly, the overspeed control device <NUM> may serve as an independent means for ensuring that the rotor speed of the wind turbine <NUM> does not exceed the desired speed limit or setting.

Similar to the turbine controller <NUM>, the overspeed control device <NUM> may, in several embodiments, correspond to a processor-based device, such as a computing device or any combination of computing devices. In such embodiments, the overspeed control device <NUM> may include one or more processor(s) and associated memory configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like disclosed herein). For instance, the memory device(s) may be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the overspeed control device <NUM> to perform various computer-implemented functions including, but not limited to, any of the control functions described herein. It should be appreciated that the overspeed control device <NUM> may also include any suitable hardware that allows the overspeed control device <NUM> to function as described herein. For instance, the instructions or logic for the overspeed control device <NUM> may, in one embodiment, be implemented by hard-wired logic or other circuitry.

As will be described below with reference to <FIG>, the overspeed control device <NUM> may, in several embodiments, be configured to receive a dynamic overspeed setting for the wind turbine <NUM> from the turbine controller <NUM>. Thus it should be appreciated that the overspeed control device <NUM> may be configured to be communicatively coupled to the turbine controller <NUM> via any suitable communicative link. For instance, in one embodiment, a wired connection may be provided between the overspeed control device <NUM> and the turbine controller <NUM>. In another embodiment, the overspeed control device <NUM> and the turbine controller <NUM> may be configured to communicate via a wireless connection using any suitable wireless communications protocol.

Additionally, it should be appreciated that, for purposes of illustration, the overspeed control device <NUM> is shown in <FIG> as being located within the same control box or panel as the turbine controller <NUM>. However, in other embodiments, the overspeed control device <NUM> may be located at any other suitable location relative to the turbine controller <NUM>, such as at any other location on and/or within the nacelle <NUM>, any other location on and/or within another component of the wind turbine <NUM> and/or at a location external to the wind turbine <NUM>.

Referring now to <FIG>, schematic diagram of one embodiment of an overspeed monitoring system <NUM> for a wind turbine is illustrated in accordance with aspects of the present subject matter. As shown, both the turbine controller <NUM> and the overspeed control device <NUM> may be configured to receive speed signals (e.g., as indicated by arrows <NUM>) from one or more components of the wind turbine <NUM> (e.g., from the one or more speed sensor(s) <NUM>) that are associated with the current or actual rotor speed of the wind turbine <NUM>. As indicated above, in several embodiments, it may be desired or necessary to operate a wind turbine at reduced or derated rotor speeds, such as at a speed setpoint that is less than then nominal speed setpoint for the wind turbine <NUM>. In such embodiments, the speed setpoint for the wind turbine <NUM> may be set at a speed value that is less than the nominal speed setpoint, such as a value that is less than <NUM>% of the nominal rotor speed setpoint or less than <NUM>% of the nominal rotor speed setpoint or less than <NUM>% less of the nominal rotor speed setpoint or less than <NUM>% less than the nominal rotor speed setpoint.

As shown in <FIG>, the turbine controller <NUM> may, in one embodiment, be configured to implement an internal or first overspeed monitor <NUM> that monitors the current rotor speed of the wind turbine <NUM> (e.g., via speed signal <NUM>) relative to a first predetermined overspeed setting <NUM> for the wind turbine <NUM>. For instance, the first predetermined overspeed setting <NUM> may correspond to a fixed maximum speed limit that is determined based on the nominal speed setting for the wind turbine <NUM> (e.g., by setting the first predetermined overspeed setting <NUM> at a value that exceeds the nominal speed setting for the wind turbine <NUM> by a predetermined amount). When implementing the first overspeed monitor <NUM>, the turbine controller <NUM> may be configured to compare the current rotor speed of the wind turbine <NUM> to the first predetermined overspeed setting <NUM> to determine whether the rotor speed is equal to or exceeds such overspeed setting. In the event that the rotor speed is equal to or exceeds the first predetermined overspeed setting <NUM>, the turbine controller <NUM> may be configured to initiate a corrective action to adjust the operation of the wind turbine <NUM> in a manner that reduces the rotor speed to a level below the first predetermined overspeed setting <NUM>. For instance, in one embodiment, the turbine controller <NUM> may be configured to implement a controller-based shutdown sequence of the wind turbine <NUM> to initiate a controlled shutdown of the turbine <NUM>. Alternatively, the turbine controller <NUM> may be configured to initiate any other suitable corrective action that results in a reduction of the rotor speed, such as by pitching the rotor blades <NUM>, yawing the nacelle <NUM>, adjusting the torque demand on the generator <NUM> and/or activating a brake of the wind turbine <NUM>.

Additionally, the turbine controller <NUM> may also be configured to implement a calculator (e.g., as indicated by box <NUM>) that is configured to calculate a dynamic overspeed setting for the wind turbine <NUM> (e.g., indicated by arrow <NUM>) and transmit such overspeed setting <NUM> to the overspeed control device <NUM> (e.g., via the communicative link provided between the controller <NUM> and the overspeed control device <NUM>). In several embodiments, the controller <NUM> may be configured to calculate the dynamic overspeed setting <NUM> based on the current speed setpoint for the wind turbine <NUM> such that the dynamic overspeed setting <NUM> varies as a function of the current speed setpoint. For example, when the wind turbine <NUM> is being operated within a reduced speed mode, the current speed setpoint for the wind turbine <NUM> may be set at a desired rotor speed that is less than the nominal speed setpoint for the wind turbine <NUM>. In such instance, the turbine controller <NUM> may utilize the reduced speed setpoint to calculate the dynamic overspeed setting <NUM>. For example, in one embodiment, the dynamic overspeed setting <NUM> may be calculated using the following equation (Equation <NUM>): <MAT> wherein, DOS corresponds to the dynamic overspeed setting <NUM> for the wind turbine <NUM>, CSS corresponds to the current speed setpoint for the wind turbine <NUM>, and OF corresponds to an overspeed factor used by the turbine controller <NUM> to set the dynamic overspeed setting <NUM> as a function of the current speed setpoint.

It should be appreciated that, in general, the overspeed factor may correspond to any suitable value or table of value(s) that may be used to provide the desired relationship between the current speed setpoint and the dynamic overspeed setting <NUM>. For instance, in one embodiment, the overspeed factor may be selected as a value between <NUM> and <NUM> so that the dynamic overspeed setting <NUM> corresponds to a speed limit or setting that ranges from about <NUM>% to about <NUM>% higher than the current speed setpoint, such as by selecting the overspeed factor to be a value between <NUM> and <NUM> so that the dynamic overspeed setting <NUM> corresponds to a speed limit or setting that ranges from about <NUM>% to about <NUM>% higher than the current speed setpoint. It should also be appreciated that, in one embodiment, the overspeed factor used to calculate the dynamic overspeed setting may remain constant across all speed setpoints for the wind turbine. Alternatively, the overspeed factor may be varied based across one or more of the speed setpoints for the wind turbine.

It should be appreciated that, in other embodiments, the dynamic overspeed setting may be determined based on any other suitable speed-related parameter for the wind turbine. For instance, in one embodiment, the dynamic overspeed setting may be determined as a function of the current air density of the air surrounding the wind turbine. Specifically, as indicated above, a wind turbine may often be operated at a given speed setpoint based on the current air density, such as when a wind turbine is operated at a reduce speed to compensate for the higher loads caused by higher air densities. In such instances, the dynamic overspeed setting may be varied as a function of the air density, such as by correlating various air density values to corresponding dynamic overspeed settings using a look-up table or any other suitable means.

As shown in <FIG>, similar to the turbine controller <NUM>, the overspeed control device <NUM> of the disclosed system <NUM> may also be configured to implement an overspeed monitor <NUM> that monitors the current rotor speed of the wind turbine <NUM> (e.g., via speed signal <NUM>) relative to a given overspeed setting. In doing so, the overspeed control device <NUM> may be configured to receive the dynamic overspeed setting <NUM> from the turbine controller <NUM> and, based on such overspeed setting <NUM>, determine a final overspeed setting (e.g., as indicated by arrow <NUM>) to be applied for the wind turbine <NUM> (e.g., as indicated at box <NUM>). Specifically, as shown in <FIG>, the overspeed control device <NUM> may, in one embodiment, be configured to compare the dynamic overspeed setting <NUM> to a second predetermined overspeed setting (e.g., indicated by box <NUM>) stored within the overspeed control device <NUM> to a determine the lowest or minimum speed value between the two settings. In such an embodiment, the minimum overspeed setting between the dynamic overspeed setting <NUM> and the second predetermined overspeed setting <NUM> may then be set as the final overspeed setting <NUM> to be applied within the overspeed monitor <NUM>.

When implementing the overspeed monitor <NUM>, the overspeed control device <NUM> may be configured to compare the final overspeed setting <NUM> with the current rotor speed to determine whether the rotor speed is equal to or exceeds the overspeed setting <NUM>. In the event that the rotor speed is equal to or exceeds the final overspeed setting <NUM>, the overspeed control device <NUM> may be configured to initiate a corrective or control action to adjust the operation of the wind turbine <NUM> in a manner that reduces the rotor speed to a level below the applicable overspeed setting <NUM>. For instance, as shown in <FIG>, the overspeed control device <NUM> may, in one embodiment, be configured to activate a safety chain (e.g., at box <NUM>) that, in turn, initiates a non-controller-based shutdown sequence so as to implement an immediate shutdown of the turbine <NUM>. Specifically, when the safety chain is activated, the turbine controller <NUM> may be decoupled from the other wind turbine components or otherwise rendered incapable of performing its conventional control functions such that the wind turbine <NUM> may be shutdown independent of the turbine controller <NUM>. Alternatively, the overspeed control device <NUM> may be configured to initiate any other suitable corrective action that results in a reduction of the rotor speed, such as by simply pitching the rotor blades <NUM>, yawing the nacelle <NUM>, adjusting the torque demand on the generator <NUM> and/or activating a brake of the wind turbine <NUM>.

It should be appreciated that the second predetermined overspeed setting <NUM> may generally correspond to a fixed maximum speed limit that is determined based on the nominal speed setting for the wind turbine <NUM> (e.g., by setting the second predetermined overspeed setting <NUM> at a value that exceeds the nominal speed setting for the wind turbine <NUM> by a predetermined amount). For instance, in one embodiment, the second predetermined overspeed setting <NUM> may correspond to the nominal speed setpoint for the wind turbine <NUM> multiplied by a given overspeed factor (e.g., a value ranging from <NUM> to <NUM>). It should also be appreciated that the second predetermined overspeed setting <NUM> may, in several embodiments, differ from the first predetermined overspeed setting <NUM>. For instance, in one embodiment, the first predetermined overspeed setting <NUM> used by the turbine controller <NUM> may be equal to a speed limit or value that is less than the speed limit or value corresponding to the second predetermined overspeed setting <NUM>.

By calculating the dynamic overspeed setting <NUM> based on a current speed-related parameter of the wind turbine, such as the current speed setpoint for the wind turbine <NUM> or the current air density, the disclosed system <NUM> may adjust the overspeed control settings applied by the overspeed control device <NUM> in order to accommodate instances in which the wind turbine <NUM> is being operated at reduced speeds. For instance, by scaling down the dynamic overspeed setting <NUM> as the speed setpoint for the wind turbine <NUM> is reduced, the dynamic overspeed setting <NUM> may be equal to a speed limit or value that is less than the speed limit or value corresponding to the second predetermined overspeed setting <NUM> when the wind turbine <NUM> is operating at a speed setpoint that is less than its nominal speed setpoint. In such instance, the final overspeed setting <NUM> applied by the overspeed control device <NUM> may correspond to the dynamic overspeed setting <NUM>, thereby allowing the control device <NUM> to adapt its control functionality to the reduced rotor speeds. Accordingly, in a situation in which the turbine controller <NUM> fails while the wind turbine <NUM> is operating in a reduced speed mode, the overspeed control device <NUM> may be allowed to activate the safety chain <NUM> to implement an immediate shutdown of the wind turbine <NUM> prior to the rotor speed reaching and/or exceeding the higher, second predetermined overspeed setting <NUM>, thereby preventing an extreme loading condition on the wind turbine <NUM>.

Referring now to <FIG>, a variation of the embodiment of the overspeed monitoring system <NUM> described above with reference to <FIG> is illustrated in accordance with aspects of the present subject matter. In general, the overspeed monitoring system <NUM> shown in <FIG> is configured the same as the system <NUM> described above. However, in addition to the overspeed control device <NUM> being configured to adjust its final overspeed setting <NUM> based on the dynamic overspeed setting <NUM> received from the turbine controller <NUM>, the overspeed control device <NUM> may also be configured to perform a "watch dog" function for the turbine controller <NUM>. Specifically, as shown in <FIG>, the overspeed control device <NUM> may be configured to continuously monitor the health or operational status of the turbine controller <NUM> (e.g., as indicated at box <NUM>) based on "life sign" signals received from the controller <NUM> (e.g., indicated by arrow <NUM>). For example, the turbine controller <NUM> may be configured to periodically transmit a "life sign" signal <NUM> to the overspeed control device <NUM> (e.g., every <NUM> microseconds) that provides an indication of whether the turbine controller <NUM> is operating properly. For instance, the controller <NUM> may be configured to transmit a "life sign" signal <NUM> at a given frequency that toggles between a value of zero and a value of one. In the event that the overspeed control device <NUM> does not receive the "life sign" signal <NUM> at the required frequency and/or if the signal <NUM> is not properly toggled between the appropriate values, the overspeed control device <NUM> may determine that the turbine controller <NUM> is not functioning properly. Thereafter, the overspeed control device <NUM> may be configured to activate the safety chain <NUM> to initiate an immediate shutdown of the wind turbine <NUM>.

It should be appreciated that, although the turbine controller <NUM> and the overspeed control device <NUM> of the disclosed system <NUM> are described above with reference to <FIG> and <FIG> as performing specific control functions, each individual control device <NUM>, <NUM> may be configured to perform any of the functions described above. For instance, in an alternative embodiment, the overspeed control device <NUM> may be configured to calculate the dynamic overspeed setting <NUM> based on a current speed-related parameter for the wind turbine such as the current speed setpoint or the current air density. Similarly, in another alternative embodiment, the turbine controller <NUM> may be configured to implement all of the functions of the overspeed control device <NUM>.

Referring now to <FIG>, a flow diagram of one embodiment of a method for overspeed monitoring of a wind turbine is illustrated in accordance with aspects of the present subject matter. In general, the method <NUM> will be described herein with reference to the system <NUM> described above with reference to <FIG> and <FIG>. However, it should be appreciated by those of ordinary skill in the art that the disclosed method <NUM> may be implemented within any other system. 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 in , at (<NUM>), the method <NUM> includes monitoring an actual rotor speed of the wind turbine while the wind turbine is operating at a current speed setpoint. For instance, as indicated above, the overspeed control device <NUM> may be configured to monitor the rotor speed of the wind turbine based on rotor speed signals <NUM> received from one or more components of the wind turbine <NUM> (e.g., the speed sensor(s) <NUM>).

Additionally, at (<NUM>), the method <NUM> includes referencing a dynamic overspeed setting for the wind turbine. Specifically, as indicated above, the turbine controller <NUM> may, in one embodiment, be configured to calculate a dynamic overspeed setting <NUM> based on a current speed-related parameter of the wind turbine <NUM> (e.g., the current speed setpoint or the current air density) and transmit the overspeed setting <NUM> to the overspeed control device <NUM>. In such an embodiment, the overspeed control device <NUM> may be configured to reference the dynamic overspeed setting <NUM> received from the turbine controller <NUM> to determine the final overspeed setting (e.g., as indicated below).

Moreover, at (<NUM>), the method <NUM> includes determining a final overspeed setting to be applied for the wind turbine based on a comparison between the dynamic overspeed setting and a predetermined overspeed setting for the wind turbine. The overspeed control device is configured to select the final overspeed setting as the minimum value between the dynamic overspeed setting and the predetermined overspeed setting.

Referring still to <FIG>, at (<NUM>), the method <NUM> includes comparing the actual rotor speed of the wind turbine to the final overspeed setting. Additionally, at (<NUM>), the method <NUM> includes initiating a control action to adjust an operation of the wind turbine in a manner that reduces the actual rotor speed when the actual rotor speed is equal to or exceeds the final overspeed setting. For example, as described above, the overspeed control device <NUM> may be configured to activate a safety chain <NUM> to initiate a shutdown sequence of the wind turbine when it is determined that the actual rotor speed is equal to or exceeds the final overspeed setting applied by the overspeed control device <NUM>.

Claim 1:
A method (<NUM>) for overspeed monitoring of a wind turbine (<NUM>), the method (<NUM>) comprising:
monitoring, with a control device (<NUM>), an actual rotor speed of the wind turbine (<NUM>) while the wind turbine (<NUM>) is operating at a current speed setpoint;
referencing, with the control device (<NUM>), a dynamic overspeed setting (<NUM>) for the wind turbine (<NUM>);
determining, with the control device (<NUM>), a final overspeed setting (<NUM>) to be applied for the wind turbine (<NUM>) based on a comparison between the dynamic overspeed setting (<NUM>) and a predetermined overspeed setting for the wind turbine (<NUM>), wherein determining the final overspeed setting for the wind turbine (<NUM>) comprises selecting the final overspeed setting as a minimum of the dynamic overspeed setting (<NUM>) and the predetermined overspeed setting;
comparing, with the control device (<NUM>), the actual rotor speed of the wind turbine (<NUM>) to the final overspeed setting (<NUM>); and
when the actual rotor speed is equal to or exceeds the final overspeed setting (<NUM>), initiating, with the control device (<NUM>), a control action to adjust an operation of the wind turbine (<NUM>) in a manner that reduces the actual rotor speed.