FIELD
[0001] The present invention relates generally to wind turbines, and more
particularly, to systems and methods for dynamically adjusting a rate of change of a
rotor speed set point of the wind turbine during shutdown.
BACKGROUND
[0002] 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
generator, a gearbox, a nacelle, and a rotor. The rotor typically includes a rotatable
hub having one or more rotor blades attached thereto. A pitch bearing is typically
configured operably between the hub and a blade root of the rotor blade to allow for
rotation about a pitch axis. 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.
[0003] During wind turbine operation, there are various scenarios that require the
wind turbine to be shut down. Such shutdown scenarios may occur, for example, due
to regularly-scheduled maintenance, blade pitch faults, fatigue loading, extreme
loading, grid events, and/or converter trips. Conventional wind turbine controllers use
a constant ramp rate for reducing the rotor speed set point during wind turbine
shutdown. As such, the rotor speed set point ramps down according to the constant
ramp rate to force the controller to take actions to reduce the actual rotor speed of the
wind turbine. The constant ramp rate, however, fails to address potential
stresses/loading of the wind turbine during the shutdown period.
[0004] Accordingly, an improved system and method for dynamically adjusting
the ramp rate of the rotor speed set point of the wind turbine during shutdown so as to
maintain the structural loads within acceptable levels would be welcomed in the art.
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BRIEF DESCRIPTION OF THE INVENTION
[0005] Aspects and advantages of the invention will be set forth in part in the
following description, or may be obvious from the description, or may be learned
through practice of the invention.
[0006] In one aspect, the present disclosure is directed to a method for operating a
wind turbine. The method includes initiating, via the controller, a shutdown
procedure or a curtailment procedure of the wind turbine. During the shutdown
procedure or the curtailment procedure of the wind turbine, the method includes
dynamically adjusting a rate of change of a rotor speed set point as a function of a
rotor-speed tracking error, the rotor-speed tracking error being equal to a difference
between an actual speed of the wind turbine and the rotor speed set point.
[0007] In one embodiment, for example, the actual speed of the wind turbine may
correspond to the actual rotor speed. In such embodiments, the method may include
determining the actual rotor speed of the wind turbine by measuring, via one or more
sensors, a generator speed of the wind turbine and dividing the generator speed by a
gearbox ratio of a gearbox of the wind turbine.
[0008] In another embodiment, dynamically adjusting the rate of change of the
speed set point as a function of the speed tracking error may include decreasing the
rate of change of the speed set point from an initial rate of change to a reduced rate of
change when the actual rotor speed is greater than the speed set point. In such
embodiments, the method may also include limiting the decreasing of the rate of
change of the speed set point to a predetermined minimum value. In addition, the
method may further include increasing the reduced rate of change of the speed set
point to the initial rate of change when the actual rotor speed approaches the speed set
point so as to expedite a stopping of a rotor of the wind turbine.
[0009] In further embodiments, dynamically adjusting the rate of change of the
speed set point as a function of the speed tracking error may include maintaining the
rate of change of the speed set point at an initial rate of change when the actual rotor
speed is equal to the speed set point. Similarly, in additional embodiments,
dynamically adjusting the rate of change of the speed set point as a function of the
speed tracking error further comprises maintaining the rate of change of the speed set
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point at an initial rate of change when the actual rotor speed is less than the speed set
point.
[0010] In particular embodiments, the speed set point may be a rotor speed set
point, a generator speed set point, or a rotational speed set point within a gearbox of
the wind turbine.
[0011] In another aspect, the present disclosure is directed to a system for
operating a wind turbine. The system includes a controller having at least one
processor. The processor is configured to perform a plurality of operations, including
but not limited to initiating a shutdown procedure or a curtailment procedure of the
wind turbine and during the shutdown procedure or the curtailment procedure of the
wind turbine, dynamically adjusting a rate of change of the speed set point as a
function of a speed tracking error. It should be understood that the system may be
further configured to implement any of the additional steps and/or may include any of
the additional features as described herein.
[0012] In yet another aspect, the present disclosure is directed to a method for
shutting down or curtailing a wind turbine. During normal operation of the wind
turbine, the method includes operating, via a controller, the wind turbine according to
a speed set point. The method also includes receiving, via the controller, a command
to shut down the wind turbine or to curtail operation of the wind turbine. In response
to receiving the command, the method includes initiating, via the controller, a
shutdown procedure or a curtailment procedure of the wind turbine. During the
shutdown procedure or the curtailment procedure of the wind turbine, the method
includes dynamically adjusting a rate of change of the speed set point as a function of
a speed tracking error, which corresponds to a difference between an actual rotor
speed of the wind turbine and the speed set point. It should be understood that the
method may further include any of the additional steps and/or features as described
herein.
[0013] These and other features, aspects and advantages of the present invention
will become better understood with reference to the following description and
appended claims. The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate the embodiments of the invention and,
together with the description, serve to explain the principles of the invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A full and enabling disclosure of the present invention, including the best
mode thereof, directed to one of ordinary skill in the art, is set forth in the
specification, which makes reference to the appended figures, in which:
[0015] FIG. 1 illustrates a perspective view of one embodiment of a wind turbine
according to the present disclosure;
[0016] FIG. 2 illustrates a simplified, internal view of one embodiment of a
nacelle of a wind turbine according to the present disclosure;
[0017] FIG. 3 illustrates a schematic diagram of one embodiment of a controller
according to the present disclosure;
[0018] FIG. 4 illustrates a flow diagram of one embodiment of a method for
operating a wind turbine during shutdown according to the present disclosure;
[0019] FIG. 5 illustrates a graph of the rotor-speed set point ramp rate in
rpm/second (y-axis) versus the rotor-speed tracking error in rpm (x-axis); and
[0020] FIG. 6 illustrates a flow diagram of one embodiment of a method for
shutting down or curtailing a wind turbine according to the present disclosure.
DETAILED DESCRIPTION
[0021] Reference now will be made in detail to embodiments of the invention,
one or more examples of which are illustrated in the drawings. Each example is
provided by way of explanation of the invention, not limitation of the invention. In
fact, it will be apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing from the scope or
spirit of the invention. For instance, features illustrated or described as part of one
embodiment can be used with another embodiment to yield a still further
embodiment. Thus, it is intended that the present invention covers such modifications
and variations as come within the scope of the appended claims and their equivalents.
[0022] Some of the braking procedures used during a wind turbine shutdown
procedure use closed-loop controls to track the speed set point. At the start of a
shutdown procedure, the initial rotor-speed response depends on the circumstances
that triggered that shutdown. In one extreme, a fault in one of the rotor blades may
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prevent this blade from pitching while the other blades must pitch towards feather to
bring the rotor speed down. On the opposite extreme, a grid fault may cause the loss
of counter-torque such that the rotor speed starts increasing. Under all scenarios, the
goal of a controlled shutdown is to provide a mechanism for safe reduction of the
rotor speed, such that the structural loads on the tower, main shaft, rotor blades,
and/or other components are mitigated.
[0023] Speed regulation is an important part of the turbine shutdown, but the pitch
actuators also need to address structural loads during the shutdowns. If the rotorspeed set point ramps down too fast, while the rotor speed is still increasing due to a
loss of counter-torque, then the aggressive pitch action may be harmful to the turbine
tower, for instance. To mitigate this problem, the ramp rate of the speed set point can
be configured to vary as a function of the speed tracking error. When the actual speed
can keep up with the desired rate of speed reduction, then the speed set point
continues ramping down at the original ramp rate. Otherwise, the rate of change in
the speed set point reduces towards a minimum ramp rate.
[0024] Referring now to the drawings, FIG. 1 illustrates a perspective view of one
embodiment of a wind turbine 10 that may implement the control technology
according to the present disclosure is illustrated. As shown, the wind turbine 10
generally includes a tower 12 extending from a support surface 14, a nacelle 16
mounted on the tower 12, and a rotor 18 coupled to the nacelle 16. The rotor 18
includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending
outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18
includes three rotor blades 22. However, in an alternative embodiment, the rotor 18
may include more or less than three rotor blades 22. Each rotor blade 22 may be
spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to
be transferred from the wind into usable mechanical energy, and subsequently,
electrical energy. For instance, the hub 20 may be rotatably coupled to an electric
generator 24 (FIG. 2) positioned within the nacelle 16 to permit electrical energy to be
produced.
[0025] The wind turbine 10 may also include a wind turbine controller 26
centralized within the nacelle 16. However, in other embodiments, the controller 26
may be located within any other component of the wind turbine 10 or at a location
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outside the wind turbine. Further, the controller 26 may be communicatively coupled
to any number of the components of the wind turbine 10 in order to control the
operation of such components. As such, the controller 26 may include a computer or
other suitable processing unit. Thus, in several embodiments, the controller 26 may
include suitable computer-readable instructions that, when implemented, configure
the controller 26 to perform various different functions, such as receiving,
transmitting and/or executing wind turbine operating signals. Accordingly, the
controller 26 may generally be configured to control the various operating modes
(e.g., start-up or shut-down sequences) and/or control various components of the wind
turbine 10 as will be discussed in more detail below.
[0026] Referring now to FIG. 2, a simplified, internal view of one embodiment of
the nacelle 16 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, the
generator 24 may be coupled to the rotor 18 for producing electrical power from the
rotational energy generated by the rotor 18. For example, as shown in the illustrated
embodiment, the rotor 18 may include a rotor shaft 34 coupled to the hub 20 for
rotation therewith. The rotor shaft 34 may, in turn, be rotatably coupled to a generator
shaft 36 of the generator 24 through a gearbox 38. As is generally understood, the
rotor shaft 34 may provide a low speed, high torque input to the gearbox 38 in
response to rotation of the rotor blades 22 and the hub 20. The gearbox 38 may then
be configured to convert the low speed, high torque input to a high speed, low torque
output to drive the generator shaft 36 and, thus, the generator 24.
[0027] Each rotor blade 22 may also include a pitch adjustment mechanism 32
configured to rotate each rotor blade 22 about its pitch axis 28. Further, each pitch
adjustment mechanism 32 may include a pitch drive motor 40 (e.g., any suitable
electric, hydraulic, or pneumatic motor), a pitch drive gearbox 42, and a pitch drive
pinion 44. In such embodiments, the pitch drive motor 40 may be coupled to the pitch
drive gearbox 42 so that the pitch drive motor 40 imparts mechanical force to the
pitch drive gearbox 42. Similarly, the pitch drive gearbox 42 may be coupled to the
pitch drive pinion 44 for rotation therewith. The pitch drive pinion 44 may, in turn,
be in rotational engagement with a pitch bearing 46 coupled between the hub 20 and a
corresponding rotor blade 22 such that rotation of the pitch drive pinion 44 causes
rotation of the pitch bearing 46. Thus, in such embodiments, rotation of the pitch
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drive motor 40 drives the pitch drive gearbox 42 and the pitch drive pinion 44,
thereby rotating the pitch bearing 46 and the rotor blade 22 about the pitch axis 28.
Similarly, the wind turbine 10 may include one or more yaw drive mechanisms 54
communicatively coupled to the controller 26, with each yaw drive mechanism(s) 54
being configured to change the angle of the nacelle 16 relative to the wind (e.g., by
engaging a yaw bearing 55 of the wind turbine 10).
[0028] Still referring to FIG. 2, the wind turbine 10 may also include one or more
sensors 48, 50, 52 for measuring various wind and/or wind turbine condition(s) as
described herein. For example, in various embodiments, the sensors 48, 50, 52 may
be wind parameter sensors configured to measure various wind parameters, such as
wind speed, wind gusts, wind acceleration, wind veer, wind peaks, wind turbulence,
wind shear, changes in wind direction, wakes, air density, or any other wind
parameter. Further, the sensors 48, 50, 52 may be located at any suitable location on
or around the wind turbine 10 (e.g. on the ground near the wind turbine 10, on the
nacelle 16, or on a meteorological mast of the wind turbine 10) so as to measure
various wind turbine parameters (such as rotor speed or generator speed). In addition,
it should be understood that any number and/or type of sensors may be employed.
For example, the sensors may be Micro Inertial Measurement Units (MIMUs), strain
gauges, accelerometers, pressure sensors, angle of attack sensors, vibration sensors,
Light Detecting and Ranging (LIDAR) sensors, camera systems, fiber optic systems,
anemometers, wind vanes, Sonic Detection and Ranging (SODAR) sensors, infra
lasers, radiometers, pitot tubes, rawinsondes, other optical sensors, and/or any other
suitable sensors.
[0029] Referring now to FIG. 3, a block diagram of various components of the
controller 26 according to the present disclosure is illustrated. As shown, the
controller 26 may include one or more processor(s) 58, and associated memory
device(s) 60 configured to perform a variety of computer-implemented functions
(e.g., performing the methods, steps, calculations and the like and storing relevant
data as disclosed herein). Additionally, the controller 26 may also include a
communications module 62 to facilitate communications between the controller 26
and the various components of the wind turbine 10. For example, as shown, the
communications module 62 may include a sensor interface 64 (e.g., one or more
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analog-to-digital converters) to permit signals transmitted from the sensors 48, 50, 52
to be converted into signals that can be understood and processed by the processor 58.
It should be appreciated that the sensors 48, 50, 52 may be communicatively coupled
to the communications module 62 using any suitable means. For example, as shown
in FIG. 3, the sensors 48, 50, 52 are coupled to the sensor interface 64 via a wired
connection. However, in other embodiments, the sensors 48, 50, 52 may be coupled
to the sensor interface 64 via a wireless connection, such as by using any suitable
wireless communications protocol known in the art.
[0030] 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) 60 may generally include 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)
60 may generally be configured to store suitable computer-readable instructions that,
when implemented by the processor(s) 58, configure the controller 26 to perform
various functions as described herein.
[0001] Referring now to FIG. 4, a flow chart of one embodiment of a method 100
for operating a wind turbine is illustrated. In general, the method 100 will be
described herein with reference to the wind turbine 10 of FIGS. 1-3. However, it
should be appreciated that the disclosed method 100 may be implemented with wind
turbines having any other suitable configurations. In addition, although FIG. 4
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.
[0002] As shown at (102), the method 100 may include operating, via the
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controller 26, the wind turbine 10 according to a speed set point during normal
operation of the wind turbine 10. For example, in particular embodiments, the speed
set point may be a rotor speed set point, a generator speed set point, or a rotational
speed set point within a gearbox of the wind turbine 10. As shown at (104), the
method 100 may include receiving, via the controller 26, a command to shut down the
wind turbine 10 or to curtail operation of the wind turbine 10. In response to
receiving the command, as shown at (106), the method 100 may include initiating, via
the controller 26, a shutdown procedure or a curtailment procedure of the wind
turbine 10. During the shutdown procedure or the curtailment procedure of the wind
turbine 10, as shown at (108), the method 100 includes dynamically adjusting a rate of
change of the speed set point as a function of a speed tracking error, which
corresponds to a difference between an actual rotor speed of the wind turbine and the
speed set point. Thus, in one embodiment, the method 100 may also include
measuring the actual rotor speed via one or more of the sensors 48, 50, 52.
[0003] The method 100 of the present disclosure can be better understood with
respect to FIG. 5. As shown, FIG. 5 illustrates a graph 150 of the rotor-speed set
point ramp rate (also referred to herein as the rate of change) in rpm/second (y-axis)
versus the rotor-speed tracking error in rpm (x-axis). Further, as shown, conventional
shutdown procedures implemented a constant, nominal ramp rate 152. In contrast, the
rotor-speed set point ramp rate 154 of the present disclosure varies as a function of the
rotor-speed tracking error. In addition, as shown, the rotor-speed set point ramp rate
154 of the present disclosure is ramped down from an initial, maximum ramp rate 156
to a minimum ramp rate 158.
[0004] Accordingly, in certain embodiments, the controller 26 may be configured
to dynamically adjust the rate of change of the rotor speed set point by decreasing the
rate of change of the rotor speed set point from an initial rate of change (e.g. the
maximum ramp rate 156) to a reduced rate of change (e.g. the minimum ramp rate
158) when the actual rotor speed is greater than the rotor speed set point. In such
embodiments, the method 100 may also include limiting the decreasing of the rate of
change of the rotor speed set point to a predetermined minimum value (i.e. the value
represented by 158). In addition, in further embodiments, the method 100 may further
include increasing the reduced rate of change of the rotor speed set point back to the
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initial rate of change when the actual rotor speed approaches the speed set point so as
to expedite a stopping of a rotor of the wind turbine 10.
[0005] In further embodiments, the controller 26 may be configured to
dynamically adjust the rate of change of the speed set point by maintaining the rate of
change of the speed set point at an initial rate of change (e.g. the maximum ramp rate
156) when the actual rotor speed is equal to the speed set point. Similarly, in
additional embodiments, the controller 26 may be configured to dynamically adjust
the rate of change of the speed set point by maintaining the rate of change of the
speed set point at an initial rate of change when the actual rotor speed is less than the
speed set point.
[0006] Referring now to FIG. 6, a flow chart of one embodiment of a method 200
for shutting down or curtailing a wind turbine is illustrated. In general, the method
200 will be described herein with reference to the wind turbine 10 of FIGS. 1-3.
However, it should be appreciated that the disclosed method 200 may be implemented
with wind turbines having any other suitable configurations. In addition, although
FIG. 6 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.
[0007] As shown at (202), the method 200 may include initiating, via the
controller 26, a shutdown procedure or a curtailment procedure of the wind turbine
10. During the shutdown procedure or the curtailment procedure of the wind turbine
10, as shown at (204), the method 200 includes dynamically adjusting a rate of change
of a rotor speed set point as a function of a rotor-speed tracking error. As mentioned,
the rotor-speed tracking error corresponds to a difference between an actual rotor
speed of the wind turbine and the rotor speed set point (e.g. the measured rotor speed
minus the rotor speed set point). Thus, the method 200 provides a mechanism for safe
reduction of the rotor speed, such that the structural loads on the tower 12, main shaft
34, rotor blades 22, and/or other components of the wind turbine 10 are mitigated.
[0008] This written description uses examples to disclose the invention, including
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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. 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 include 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 languages
of the claims.

We claim:
1. A method (100) for operating a wind turbine (10), the method (100)
comprising:
initiating, via a controller (26), a shutdown procedure or a curtailment
procedure of the wind turbine (10); and,
during the shutdown procedure or the curtailment procedure of the wind
turbine (10), dynamically adjusting a rate of change of a speed set point as a function
of a speed tracking error, the speed tracking error being equal to a difference between
an actual speed of the wind turbine (10) and a speed set point of the wind turbine (10).
2. The method (100) of claim 1, wherein the actual speed of the wind
turbine (10) comprises the actual rotor speed, the method (100) further comprising
determining the actual rotor speed of the wind turbine (10) by measuring, via one or
more sensors, a generator speed of the wind turbine (10) and dividing the generator
speed by a gearbox ratio of a gearbox of the wind turbine (10).
3. The method (100) of claims 1 or 2, wherein dynamically adjusting the
rate of change of the speed set point as a function of the speed tracking error further
comprises decreasing the rate of change of the speed set point from an initial rate of
change to a reduced rate of change when the actual speed is greater than the speed set
point.
4. The method (100) of claim 3, further comprising limiting the
decreasing of the rate of change of the speed set point to a predetermined minimum
value.
5. The method (100) of claim 3, further comprising increasing the
reduced rate of change of the speed set point to the initial rate of change when the
actual speed approaches the speed set point so as to expedite a stopping of a rotor of
the wind turbine (10).
6. The method (100) of any of the preceding claims, wherein dynamically
adjusting the rate of change of the speed set point as a function of the speed tracking
error further comprises maintaining the rate of change of the speed set point at an
initial rate of change when the actual speed is equal to the speed set point.
7. The method (100) of any of the preceding claims, wherein dynamically
adjusting the rate of change of the speed set point as a function of the speed tracking
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error further comprises maintaining the rate of change of the speed set point at an
initial rate of change when the actual speed is less than the speed set point.
8. The method (100) of any of the preceding claims, wherein the speed
set point comprises at least one of a rotor speed set point, a generator speed set point,
or a rotational speed set point within a gearbox of the wind turbine (10).
9. A system for operating a wind turbine (10), the system comprising:
a controller (26) having at least one processor (58), the processor (58)
configured to perform a plurality of operations, the plurality of operations comprising:
initiating a shutdown procedure or a curtailment procedure of the wind
turbine (10); and,
during the shutdown procedure or the curtailment procedure of the
wind turbine (10), dynamically adjusting a rate of change of the speed set
point as a function of a speed tracking error, the speed tracking error
corresponding to a difference between an actual speed of the wind turbine (10)
and the speed set point.
10. The system of claim 9, wherein the actual speed of the wind turbine
(10) comprises the actual rotor speed, the system further comprising via one or more
sensors for measuring a generator speed of the wind turbine (10), the plurality of
operations further comprising determining the actual rotor speed by dividing the
generator speed by a gearbox ratio of a gearbox of the wind turbine (10).
11. The system of claims 9 or 10, wherein dynamically adjusting the rate
of change of the speed set point as a function of the speed tracking error further
comprises decreasing the rate of change of the speed set point from an initial rate of
change to a reduced rate of change when the actual speed is greater than the speed set
point.
12. The system of claim 11, further comprising limiting the decreasing of
the rate of change of the speed set point to a predetermined minimum value.
13. The system of claim 11, further comprising increasing the reduced rate
of change of the speed set point to the initial rate of change when the actual speed
approaches the speed set point so as to expedite a stopping of a rotor of the wind
turbine (10).
14. The system of claims 9, 10, 11, 12, or 13, wherein dynamically
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adjusting the rate of change of the speed set point as a function of the speed tracking
error further comprises maintaining the rate of change of the speed set point at an
initial rate of change when the actual speed is equal to the speed set point.
15. The system of claims 9, 10, 11, 12, 13, or 14, wherein dynamically
adjusting the rate of change of the speed set point as a function of the speed tracking
error further comprises maintaining the rate of change of the speed set point at an
initial rate of change when the actual speed is less than the speed set point.