SYSTEM AND METHOD FOR APPLYING A PITCH MOTOR BRAKING
TORQUE TO A WIND TURBINE ROTOR BLADE
FIELD
[0001] The present disclosure relates in general to wind turbines, and more
particularly to systems and methods for applying a pitch motor braking torque to a
rotor blade of the wind turbine.
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 one or more rotor blades. The nacelle includes a
rotor assembly coupled to the gearbox and to the generator. The rotor assembly and
the gearbox are mounted on a bedplate support frame located within the nacelle. The
one or more 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 and the electrical energy may be transmitted to a converter
and/or a transformer housed within the tower and subsequently deployed to a utility
grid. Modern wind power generation systems typically take the form of a wind farm
having multiple such wind turbine generators that are operable to supply power to a
transmission system providing power to an electrical grid.
[0003] Typically, the rotor blades are rotated or pitched about a pitch axis via a
pitch control system that is driven by a pitch motor which is powered by a pitch
power converter. However, in various scenarios, such as a failure of the pitch power
converter, it may be necessary to power the pitch control system via an alternate
energy source. During the transition from the pitch power converter to the alternate
energy source, there may be a period during which there is no torque applied by the
pitch motor. As such, gravity and/or inertia may cause an uncontrolled rotation of the
rotor blade to an undesirable loaded orientation. This, in turn, may result in an
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overloaded condition of the rotor blade, thereby leading to component and/or wind
turbine failure.
[0004] In addition to the overloaded condition, the uncontrolled rotation of the
rotor blade to undesirable loaded orientation may also result in the pitch motor
generating an electric current. This electric current may flow to the alternate energy
source and interfere with the powering of the pitch control system by the alternate
energy source. As such, it may be desirable to control the rotation of a rotor blade
while transitioning between the pitch power converter and the alternate energy source.
[0005] Thus, the art is continuously seeking new and improved systems for
restricting the uncontrolled rotation of the rotor blade to an undesirable loaded
orientation while transitioning to the alternate energy source. Accordingly, the
present disclosure is directed to systems and methods for applying a pitch motor
braking torque to the rotor blade.
BRIEF DESCRIPTION
[0006] 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.
[0007] In one aspect, the present disclosure is directed to a method for applying a
pitch motor braking torque to a rotor blade of a wind turbine. The wind turbine may
include a pitch control system operably coupled to the rotor blade for rotating the
rotor blade about a pitch axis. The method may include initiating a transition of the
pitch control system from a first operational mode to an emergency operational mode.
The pitch motor of the pitch control system may have an absence of an supply current
during the transition. The method may also include establishing a short-circuit across
an armature of the pitch motor so as to establish a current flow between a first
terminal and a second terminal of the pitch motor. The current flow may be generated
by the pitch motor in response to a rotation of the rotor blade about the pitch axis
when the pitch motor has the absence of supply current. In response to the current
flow being generated, the method may also include generating a braking torque in a
single direction with the pitch motor so as to allow the rotor blade to move freely to a
lesser loaded orientation to protect the turbine from damage.
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[0008] In an embodiment, the rotation of the rotor blade is a pitch-to-power
rotation.
[0009] In an additional embodiment, generating the braking torque in the single
direction may resist the pitch to power rotation of the rotor blade, and the movement
to a lesser loaded orientation may include a pitch-to-feather rotation of the rotor blade.
[0010] In an embodiment, establishing the short-circuit across the armature the
pitch motor may also include blocking, via a unidirectional switch, the current flow
path from the first terminal to the second terminal.
[0011] In an additional embodiment, initiating the transition of the pitch control
system may include opening a contactor operably coupling the pitch motor to a power
converter of the pitch control system. Opening the contactor may also initiate a
power flow from an alternate energy source to the unidirectional switch.
[0012] In a further embodiment, the unidirectional switch may be an
electro-mechanical switch.
[0013] In an embodiment, the unidirectional switch may be an electronic switch.
In such embodiments, for example, the electronic switch may include a silicone
controlled rectifier operably coupled to a gate driver circuit.
[0014] In an embodiment, the method may also include implementing the
transition of the pitch control system from the first operational mode to the emergency
operational mode by operably coupling the pitch motor to the alternate energy source.
[0015] In an embodiment, establishing the short-circuit across the armature of the
pitch motor may also include operably coupling a first lead of the unidirectional
switch to the first terminal of the pitch motor. The method may also include operably
coupling a second lead of the unidirectional switch to a series field of the pitch motor.
Coupling to the series field may establish a variable braking torque which increases
with a torque resulting from the rotation of the rotor blade.
[0016] In another aspect, the present disclosure is directed to a system for
applying a pitch braking torque to a rotor blade of a wind turbine via a pitch control
system. The pitch control system may include a pitch motor of the pitch control
system operably coupled to the rotor blade of the wind turbine. The pitch motor may
have an absence of supply current during a transition from a first operational mode of
the pitch control system to an emergency operational mode of the pitch control
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system. The system may include a first coupling between the pitch motor and a pitch
power converter when the pitch control system is in the first operational mode.
Opening the first coupling may initiate a transition of the pitch control system from
the first operational mode to the emergency operational mode. The system may also
include a second coupling between the pitch motor and an alternate energy source
when the pitch motor is in the emergency operational mode. Additionally, the system
may include a short-circuit across an armature of the pitch motor. The short-circuit
may establish a current flow between a first terminal and a second terminal of the
pitch motor. The current flow may be generated by the pitch motor in response to a
rotation of the rotor blade about the pitch axis when the pitch motor has the absence
of supply current. The pitch motor may be configured to generate a braking torque in
a single direction in response to the current generated by the rotation of the rotor
blade. The braking torque may permit the rotor blade to move freely to a lesser
loaded orientation to protect the rotor blade from damage. It should be understood
that the system may further include any of the additional features described herein.
[0017] In another aspect, the present disclosure is directed to a method for
applying a unidirectional pitch motor braking torque to a rotor blade of a wind
turbine. The wind turbine may have a pitch control system operably coupled to the
rotor blade for rotating the rotor blade about a pitch axis. The method may include
rotating the rotor blade about the pitch axis in a pitch-to-power. The method may also
include opening a contactor operably coupling a pitch motor of the pitch control
system to a pitch power converter to initiate a transition of the pitch control system
from a first operational mode to an emergency operational mode. Additionally, the
method may include establishing a unidirectional short-circuit across an armature of
the pitch motor. The method may further include generating, via the pitch motor, a
current in response to the pitch-to-power rotation of the rotor blade. The current
generated by the pitch motor may flow via the short-circuit back to the pitch motor.
In response to the current generated by the pitch-to-power rotation of the rotor blade,
the method may also include generating a braking torque in a single direction with the
pitch motor. The braking torque may resist the pitch-to-power rotation of the rotor
blade and permits a pitch-to-feather rotation of the rotor blade. It should be
understood that the method may further include any of the additional features and/or
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steps described herein.
[0018] 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 embodiments of the invention and,
together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] 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:
[0020] FIG. 1 illustrates a perspective view of one embodiment of a wind turbine
according to the present disclosure;
[0021] FIG. 2 illustrates a perspective, internal view of one embodiment of a
nacelle of a wind turbine according to the present disclosure;
[0022] FIG. 3 illustrates a wire diagram of one embodiment of a pitch control
system according to the present disclosure;
[0023] FIG. 4 illustrates a wire diagram of one embodiment of a pitch control
system according to the present disclosure;
[0024] FIG. 5 illustrates a flow diagram of one embodiment of a method for
applying a pitch motor braking torque to a rotor blade of a wind turbine according to
the present disclosure; and
[0025] FIG. 6 illustrates a flow diagram of one embodiment of a method for
applying a unidirectional pitch motor braking torque to a rotor blade of a wind turbine
according to the present disclosure.
[0026] Repeat use of reference characters in the present specification and
drawings is intended to represent the same or analogous features or elements of the
present invention.
DETAILED DESCRIPTION
[0027] 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
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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.
[0028] As used herein, the terms “first”, “second”, and “third” may be used
interchangeably to distinguish one component from another and are not intended to
signify location or importance of the individual components.
[0029] The terms “coupled,” “fixed,” “attached to,” and the like refer to both
direct coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching
through one or more intermediate components or features, unless otherwise specified
herein.
[0030] Approximating language, as used herein throughout the specification and
claims, is applied to modify any quantitative representation that could permissibly
vary without resulting in a change in the basic function to which it is related.
Accordingly, a value modified by a term or terms, such as “about”, “approximately”,
and “substantially”, are not to be limited to the precise value specified. In at least
some instances, the approximating language may correspond to the precision of an
instrument for measuring the value, or the precision of the methods or machines for
constructing or manufacturing the components and/or systems. For example, the
approximating language may refer to being within a 10 percent margin.
[0031] Here and throughout the specification and claims, range limitations are
combined and interchanged, such ranges are identified and include all the sub-ranges
contained therein unless context or language indicates otherwise. For example, all
ranges disclosed herein are inclusive of the endpoints, and the endpoints are
independently combinable with each other.
[0032] Generally, the present disclosure is directed to systems and methods for
applying a pitch motor braking torque to a rotor blade of a wind turbine. In particular,
the present disclosure includes a system and method which may resist a rotation of the
rotor blade toward an undesirable loaded orientation when a pitch motor of a pitch
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control system is unpowered. Specifically, the present disclosure may include
initiating a transition of the pitch control system from a first operational mode to an
emergency operational mode. This transition may include switching the power source
of the pitch control system from a pitch power converter to an alternate energy source.
During the transition, no current may be flowing to the pitch motor from an external
source and the pitch motor may be unable to generate a torque to control the rotation
of the rotor blade about a pitch axis. As such, a short-circuit may be established
across an armature of the pitch motor. The short-circuit may permit a current
generated by the unpowered motor in response to the uncontrolled rotation of the
rotor blade to flow back into one of at least two field windings of the pitch motor. In
response to the current flow, the pitch motor may generate a braking torque in a single
direction. The braking torque may resist the rotation of the rotor blade to the
undesirable loaded orientation (e.g., pitch-to-power) while permitting a rotation to a
lesser loaded orientation (e.g., pitch-to-feather). Resisting the rotation to a more
loaded orientation, may protect the rotor blade and the wind turbine from damage due
to overloading.
[0033] Referring now to the drawings, FIG. 1 illustrates a perspective view of one
embodiment of a wind turbine 100 according to the present disclosure. As shown, the
wind turbine 100 generally includes a tower 102 extending from a support surface
104, a nacelle 106, mounted on the tower 102, and a rotor 108 coupled to the nacelle
106. The rotor 108 includes a rotatable hub 110 and at least one rotor blade 112
coupled to and extending outwardly from the hub 110. For example, in the illustrated
embodiment, the rotor 108 includes three rotor blades 112. However, in an alternative
embodiment, the rotor 108 may include more or less than three rotor blades 112.
Each rotor blade 112 may be spaced about the hub 110 to facilitate rotating the rotor
108 to enable kinetic energy to be transferred from the wind into usable mechanical
energy, and subsequently, electrical energy. For instance, the hub 110 may be
rotatably coupled to an electric generator 118 (FIG. 2) positioned within the nacelle
106 to permit electrical energy to be produced.
[0034] Referring now to FIG. 2, a simplified, internal view of one embodiment of
the nacelle 106 of the wind turbine 100 shown in FIG. 1 is illustrated. As shown, the
generator 118 may be coupled to the rotor 108 for producing electrical power from the
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rotational energy generated by the rotor 108. For example, as shown in the illustrated
embodiment, the rotor 108 may include a rotor shaft 122 coupled to the hub 110 for
rotation therewith. The rotor shaft 122 may be rotatably supported by a main bearing
144. The rotor shaft 122 may, in turn, be rotatably coupled to a high-speed shaft 124
of the generator 118 through a gearbox 126 connected to a bedplate support frame 136
by one or more torque arms 142. As is generally understood, the rotor shaft 122 may
provide a low-speed, high-torque input to the gearbox 126 in response to rotation of
the rotor blades 112 and the hub 110. The gearbox 126 may then be configured to
convert the low-speed, high-torque input to a high-speed, low-torque output to drive
the high-speed shaft 124 and, thus, the generator 118.
[0035] Referring now to FIGS. 2-4, in an embodiment, each rotor blade 112 may
also include a pitch control system 120 configured to rotate each rotor blade 112
about its pitch axis 116. Each pitch control system 120 may also include a pitch
motor 128, a pitch drive gearbox 130, and a pitch drive pinion 132. In such
embodiments, the pitch motor(s) 128 may be coupled to the pitch drive gearbox(s)
130 so that the pitch motor(s) 128 imparts mechanical force to the pitch drive
gearbox(s) 130. Similarly, the pitch drive gearbox(s) 130 may be coupled to the pitch
drive pinion(s) 132 for rotation therewith. The pitch drive pinion(s) 132 may, in turn,
be in rotational engagement with a pitch bearing 134 coupled between the hub 110
and a corresponding rotor blade 112 such that rotation of the pitch drive pinion(s) 132
causes rotation of the pitch bearing(s) 134. Thus, in such embodiments, rotation of
the pitch motor(s) 128 drives the pitch drive gearbox(s) 130 and the pitch drive
pinion(s) 132, thereby rotating the pitch bearing(s) 134 and the rotor blade(s) 112
about the pitch axis 116.
[0036] In an embodiment, as shown particularly in FIGS. 3 and 4, the pitch
motor(s) 128 may be operably coupled to a pitch power converter 146. In at least one
embodiment, the coupling between the pitch motor(s) 128 and the pitch power
converter 146 may be a first coupling 148. The first coupling 148 may, in an
embodiment, be a contactor, a relay, a switch, a manual controller, or any other device
suitable for switching electrical power. The pitch power converter 146 delivers an
supply current to the pitch motor(s) 128 when the pitch control system(s) 120 is in at
least a first operational mode.
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[0037] In an additional embodiment, as shown, the pitch motor(s) 128 may be
operably coupled to an alternate energy source 150. In at least one embodiment, the
coupling between the pitch motor(s) 128 and the alternate energy source 150 may be a
second coupling 152. The second coupling 152 may, in an embodiment, be a
contactor, a relay, a switch, a manual controller, or any other device suitable for
switching electrical power. The alternate energy source 150 may be a battery bank, a
capacitor bank, a backup generator, and/or other source of power suitable for
providing an supply current to the pitch motor(s) 128 during an unavailability of the
supply current from the pitch power converter 146. As such, the alternate energy
source 150 delivers an supply current to the pitch motor(s) 128 when the pitch control
system(s) 120 is in an emergency operational mode.
[0038] In at least one embodiment, the pitch control system(s) 120 may be
transitioned from the first operational mode to the emergency mode in response to a
failure associated with the supply current delivered by the pitch power converter 146.
In other words, in an embodiment, a failure may reside within the pitch power
converter 146 or within a power grid coupled thereto, which may necessitate the
transition to the emergency mode. The transition may be initiated by opening the first
coupling 148. As opening the first coupling 148 decouples the pitch motor(s) 128
from the pitch power converter 146, during the transition from the first operational
mode to emergency operational mode, the pitch motor(s) 128 may have an absence of
supply current. In at least one embodiment, the pitch motor(s) 128 may have an
absence of supply current for greater than or equal to 50 milliseconds (ms) (e.g.,
greater than or equal to 100 ms). In an additional embodiment, the pitch motor(s) 128
may have an absence of supply current for less than or equal to 500 ms (e.g., less than
or equal to 300 ms). In an embodiment, the transition of the pitch control system(s)
120 from the first operational mode to an emergency operational mode may be
completed by operably coupling the pitch motor(s) 128 to the alternate energy source
150 via the second coupling 152.
[0039] It should be appreciated that the delay in the transition from the first
operational mode to the emergency operational mode, may result in a period during
which no torque is generated by the pitch motor(s) 128. In the absence of a torque
provided by the pitch motor(s) 128, the rotor blade(s) 112 may freely rotate in an
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uncontrolled manner in response to inertia and/or external forces (e.g., gravity or
wind). For example, in an embodiment wherein the rotor blade(s) 112 may be
rotating about the pitch axis 116 prior to the opening of the first coupling 148, the
rotor blade(s) 112 may continue the rotation due to inertia. In at least one
embodiment, this rotation may be a rotation toward a more aerodynamically loaded
orientation (e.g., a pitch-to-power).
[0040] Still referring to FIGS. 3 and 4, in an embodiment, the pitch motor(s) 128
may be a brushed DC motor having two field windings. One of the field windings
may be a shunt field winding 156 which is excited independent of an armature 154 of
the pitch motor 128. The other of the field windings may be a series field winding
158. The series field winding 158 may be excited by the current flowing through the
armature 154. The excitation of the series field winding 158 may be the result of the
supply current or may be the result of a current generated by the pitch motor(s) 128 in
response to an uncontrolled (e.g., unintended) rotation of the rotor blade(s) 112 about
the pitch axis 116.
[0041] As further depicted in FIGS. 3 and 4, the pitch control system(s) 120 may
also include a short-circuit 160 across the armature 154 of the pitch motor(s) 128.
The short-circuit 160 may establish a current flow between a first terminal 162 and a
second terminal 164 of the pitch motor(s) 128. The current flow may be generated by
the pitch motor(s) 128 in response to a rotation of the rotor blade(s) 112 about the
pitch axis 116. The pitch motor may, in an embodiment, be configured to generate a
braking torque in a single direction in response to the current generated by the rotation
of the rotor blade(s) 112. The braking torque may permit the rotor blade(s) 112 to
move freely to a lesser loaded orientation in order to protect the rotor blade(s) 112
from damage.
[0042] In an embodiment, the pitch control system(s) 120 may include a
unidirectional switch 166 as an element of the short-circuit 160. The unidirectional
switch 166 may be operably coupled between the first terminal 162 and the second
terminal 164 of the pitch motor(s) 128. The unidirectional switch 166 may block a
current flow path from the first terminal 162 to the second terminal 164, while
permitting a current flow from the second terminal 164 to the first terminal 162. In an
embodiment, the blocked current flow from the first terminal 162 to the second
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terminal 164 may be generated by the pitch motor(s) 128 in response to the rotation of
the rotor blade(s) 112 toward a lesser loaded orientation (e.g., a pitch-to-feather). In
an additional embodiment, the current flow which is allowed to pass through the
unidirectional switch 166 from the second terminal 164 to the first terminal 162 may
be generated by the pitch motor(s) 128 in response to a rotation of the rotor blade(s)
112 toward a more loaded orientation. It should be appreciated that the current flow
from the second terminal 164 to the first terminal 162 may result in the pitch motor(s)
128 generating the pitch motor braking torque in a single direction while allowing the
rotor blades 112 to move freely to the lesser loaded orientation. In other words, in at
least one embodiment, the uncontrolled pitch-to-power of the rotor blade(s) 112 may
generate the current in one coil of the pitch motor(s) 128 which, in turn, is utilized by
the other coil of the pitch motor(s) 128 to generate the pitch motor braking torque to
resist the pitch-to-power of the rotor blade(s) 112.
[0043] In at least one embodiment, the unidirectional switch 166 may include an
electronic switch. The electronic switch may include a silicone controlled rectifier
168 operably coupled to a gate driver circuit 170. In at least one embodiment,
opening the first coupling 148 upon the initiation of the transition of the pitch control
system(s) 120 from the first operational mode to the emergency operational mode
may initiate a power flow from the alternate energy source 150, through first coupling
148, and to the unidirectional switch 166. In other words, instantaneous with the
decoupling of the pitch motor(s) 128 from the pitch power converter 146, the
unidirectional switch 166 may be coupled to, and powered by, the alternate energy
source 150. It should be appreciated that in at least one embodiment, the
unidirectional switch 166 may be an electro-mechanical switch.
[0044] As particularly depicted in FIG. 4, in an embodiment, establishing the
short-circuit 160 across the armature 154 of the pitch motor(s) 128 may include
operably coupling a first lead 172 of the unidirectional switch 166 to the first terminal
162 of the pitch motor(s) 128, and operably coupling a second lead 174 of the
unidirectional switch 166 2 the series field 158 of the pitch motor(s) 128. It should be
appreciated that coupling the unidirectional switch 166 to the series field 158 may
incorporate the series field 158 into the short-circuit 160. It should be further
appreciated that incorporating the series field 158 into the short-circuit 160 may
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establish a variable braking torque which increases with a torque resulting from the
rotation of the rotor blade(s) 112.
[0045] Referring now to FIG. 5, a flow diagram of one embodiment of a method
200 for applying a pitch motor braking torque to a rotor blade of a wind turbine is
illustrated. The method 200 may be implemented using, for instance, the pitch control
system(s) 120 of the present disclosure discussed above with references to FIGS. 1-4.
FIG. 5 depicts steps performed in a particular order for purposes of illustration and
discussion. Those of ordinary skill in the art, using the disclosures provided herein,
will understand that various steps of the method 200, or any of the methods disclosed
herein, may be adapted, modified, rearranged, performed simultaneously, or modified
in various ways without deviating from the scope of the present disclosure.
[0046] As shown at (202), the method 200 may include initiating a transition of
the pitch control system from a first operational mode to an emergency operational
mode. The pitch motor of the pitch control system may have an absence of supply
current during the transition. As shown at (204), the method 200 may include
establishing a short-circuit across an armature of the pitch motor so as to establish a
current flow between a first terminal and a second terminal of the pitch motor. The
current flow may be generated by the pitch motor in response to a rotation of the rotor
blade about the pitch axis. In response to the current flow being generated, the
method 200 may, as shown at (206), include generating a braking torque in a single
direction with the pitch motor so as to allow the rotor blade to move freely to a lesser
loaded orientation to protect the rotor blade from damage.
[0047] Referring now to FIG. 6, a flow diagram of another embodiment of a
method 300 for applying a unidirectional pitch motor braking torque to a rotor blade
of a wind turbine is illustrated. The method 300 may be implemented using, for
instance, the pitch control system(s) 120 of the present disclosure discussed above
with references to FIGS. 1-4. FIG. 6 depicts steps performed in a particular order for
purposes of illustration and discussion. Those of ordinary skill in the art, using the
disclosures provided herein, will understand that various steps of the method 300, or
any of the methods disclosed herein, may be adapted, modified, rearranged,
performed simultaneously, or modified in various ways without deviating from the
scope of the present disclosure.
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[0048] As shown at (302), the method 300 may include rotating the rotor blade
about the pitch axis in a pitch-to-power. As shown at (304), the method 300 may
include opening a contactor operably coupling the pitch motor of the pitch control
system to the pitch power converter to initiate a transition of the pitch control
mechanism from a first operational mode to an emergency operational mode. As
shown at (306), the method 300 may include establishing a unidirectional short-circuit
across an armature of the pitch motor. As shown at (308), the method 300 may
include generating, via the pitch motor, a current in response to the pitch-to-power
rotation of the rotor blade. The current generated by the pitch motor may flow via the
short-circuit back to the pitch motor. In response to the current generated by the
pitch-to-power rotation of the rotor blade, the method 300 may as shown at (310),
include generating a braking torque in a single direction with the pitch motor. The
braking torque resists the pitch-to-power rotation of the rotor blade and permits a
pitch-to-feather rotation of the rotor blade.
[0049] Furthermore, the skilled artisan will recognize the interchangeability of
various features from different embodiments. Similarly, the various method steps and
features described, as well as other known equivalents for each such methods and
feature, can be mixed and matched by one of ordinary skill in this art to construct
additional systems and techniques in accordance with principles of this disclosure. Of
course, it is to be understood that not necessarily all such objects or advantages
described above may be achieved in accordance with any particular embodiment.
Thus, for example, those skilled in the art will recognize that the systems and
techniques described herein may be embodied or carried out in a manner that achieves
or optimizes one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught or suggested
herein.
[0050] This written description uses examples to disclose the invention, including
the best mode, and also to enable any person skilled in the art to practice the
invention, including making and using any devices or systems and performing any
incorporated methods. 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
15
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.
[0051] Further aspects of the invention are provided by the subject matter of the
following clauses:
[0052] Clause 1. A method for applying a pitch motor braking torque to a rotor
blade of a wind turbine, the wind turbine having a pitch control system operably
coupled to the rotor blade for rotating the rotor blade about a pitch axis, the method
comprising: initiating a transition of the pitch control system from a first operational
mode to an emergency operational mode, a pitch motor of the pitch control system
having an absence of supply current during the transition; establishing a short-circuit
across an armature of the pitch motor so as to establish a current flow between a first
terminal and a second terminal of the pitch motor, wherein the current flow is
generated by the pitch motor in response to a rotation of the rotor blade about the
pitch axis when the pitch motor has the absence of supply current; and in response to
the current flow being generated, generating a braking torque in a single direction
with the pitch motor so as to allow the rotor blade to move freely to a lesser loaded
orientation relative to an original orientation to protect the rotor blade from damage.
[0053] Clause 2. The method of any preceding claim, wherein the rotation of the
rotor blade is a pitch-to-power rotation.
[0054] Clause 3. The method of any preceding claim, wherein generating the
braking torque in the single direction resists the pitch-to-power rotation of the rotor
blade, and wherein the movement to a lesser loaded orientation comprises a
pitch-to-feather rotation of the rotor blade.
[0055] Clause 4. The method of any preceding claim, wherein establishing the
short-circuit across the armature of the pitch motor further comprises blocking, via a
unidirectional switch, the current flow path from the first terminal to the second
terminal.
[0056] Clause 5. The method of any preceding claim, wherein initiating the
transition of the pitch control system comprises opening a contactor operably
coupling the pitch motor to a power converter of the pitch control system, wherein
opening the contactor provides a signal to close the unidirectional switch.
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[0057] Clause 6. The method of any preceding claim, wherein the unidirectional
switch comprises an electro-mechanical switch.
[0058] Clause 7. The method of any preceding claim, wherein the unidirectional
switch comprises an electronic switch.
[0059] Clause 8. The method of any preceding claim, wherein the electronic
switch comprises a silicone controlled rectifier operably coupled to a gate driver
circuit.
[0060] Clause 9. The method of any preceding claim, further comprising:
completing the transition of the pitch control system from the first operational mode
to the emergency operational mode by operably coupling the pitch motor to the
alternate energy store.
[0061] Clause 10. The method of any preceding claim, wherein establishing the
short-circuit across the armature of the pitch motor further comprises: operably
coupling a first lead of a unidirectional switch to the first terminal of the pitch motor;
and operably coupling a second lead of the unidirectional switch to a series field of
the pitch motor, wherein coupling to the series field establishes a variable braking
torque which increases with a torque resulting from the rotation of the rotor blade.
[0062] Clause 11. A pitch control system for applying a pitch motor braking
torque to a rotor blade of a wind turbine, the pitch control system comprising: a pitch
motor operably coupled to the rotor blade of the wind turbine, the pitch motor having
an absence of supply current during a transition from a first operational mode of the
pitch control system to an emergency operational mode of the pitch control system; a
first coupling between the pitch motor and a pitch power converter when the pitch
control system is in the first operational mode, wherein opening the first coupling
initiates a transition of the pitch control system from the first operational mode to the
emergency operational mode; a short-circuit across an armature of the pitch motor,
wherein the short-circuit establishes a current flow between a first terminal and a
second terminal of the pitch motor, wherein the current flow is generated by the pitch
motor in response to a rotation of the rotor blade about the pitch axis when the pitch
motor has the absence of supply current, wherein the pitch motor is configured to
generate a braking torque in a single direction in response to the current generated by
the rotation of the rotor blade, the braking torque permitting the rotor blade to move
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freely to a lesser loaded orientation to protect the rotor blade from damage; and a
second coupling between the pitch motor and an alternate energy store when the pitch
motor is in the emergency operational mode.
[0063] Clause 12. The system of any preceding claim, wherein the short-circuit
further comprises a unidirectional switch operably coupled between the first terminal
and the second terminal of the pitch motor, the unidirectional switch blocking a
current flow path from the first terminal to the second terminal.
[0064] Clause 13. The system of any preceding claim, wherein the unidirectional
switch comprises an electronic switch.
[0065] Clause 14. The system of any preceding claim, wherein the electronic
switch comprises a silicone controlled rectifier operably coupled to a gate driver
circuit.
[0066] Clause 15. The system of any preceding claim, wherein the first coupling
is a first contactor operably coupling the silicone controlled rectifier to the alternate
energy store upon the initiation of the transition of the pitch control system from the
first operational mode to the emergency operational mode.
[0067] Clause 16. The system of any preceding claim, wherein the rotation of the
rotor blade is a pitch-to-power rotation, wherein the braking torque resists the
pitch-to-power rotation, and wherein the movement to a lesser loaded orientation is a
pitch-to-feather rotation of the rotor blade.
[0068] Clause 17. A method for applying a unidirectional pitch motor braking
torque to a rotor blade of a wind turbine, the wind turbine having a pitch control
system operably coupled to the rotor blade for rotating the rotor blade about a pitch
axis, the method comprising: rotating the rotor blade about the pitch axis in a
pitch-to-power; opening a contactor operably coupling a pitch motor of the pitch
control system to a pitch power converter to initiate a transition of the pitch control
system from a first operational mode to an emergency operational mode; establishing
a unidirectional short-circuit across an armature of the pitch motor; generating, via the
pitch motor, a current in response to the pitch-to-power rotation of the rotor blade,
wherein the current generated by the pitch motor flows via the short-circuit back to
the pitch motor; and in response to the current generated by the pitch-to-power
rotation of the rotor blade, generating a braking torque in a single direction with the
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pitch motor, wherein the braking torque resists the pitch-to-power rotation of the rotor
blade and permits a pitch-to-feather rotation of the rotor blade.
[0069] Clause 18. The method of any preceding claim, wherein establishing the
short-circuit further comprises: activating a unidirectional switch operably coupled
between a first terminal and a second terminal of the pitch motor, the unidirectional
switch blocking the current flow path from the first terminal to the second terminal.
[0070] Clause 19. The method of any preceding claim, wherein the unidirectional
switch comprises a silicone controlled rectifier operably coupled to a gate driver
circuit.
[0071] Clause 20. The method of any preceding claim, wherein opening the
contactor operably couples the silicone controlled rectifier to the alternate energy
store

WHAT IS CLAIMED IS:
1. A method for applying a pitch motor braking torque to a rotor blade of
a wind turbine, the wind turbine having a pitch control system operably coupled to the
rotor blade for rotating the rotor blade about a pitch axis, the method comprising:
initiating a transition of the pitch control system from a first operational mode
to an emergency operational mode, a pitch motor of the pitch control system having
an absence of supply current during the transition;
establishing a short-circuit across an armature of the pitch motor so as to
establish a current flow between a first terminal and a second terminal of the pitch
motor, wherein the current flow is generated by the pitch motor in response to a
rotation of the rotor blade about the pitch axis when the pitch motor has the absence
of supply current; and
in response to the current flow being generated, generating a braking torque in
a single direction with the pitch motor so as to allow the rotor blade to move freely to
a lesser loaded orientation relative to an original orientation to protect the rotor blade
from damage.
2. The method of claim 1, wherein the rotation of the rotor blade is a
pitch-to-power rotation.
3. The method of claim 2, wherein generating the braking torque in the
single direction resists the pitch-to-power rotation of the rotor blade, and wherein the
movement to a lesser loaded orientation comprises a pitch-to-feather rotation of the
rotor blade.
4. The method of claims 1-3, wherein establishing the short-circuit across
the armature of the pitch motor further comprises blocking, via a unidirectional
switch, the current flow path from the first terminal to the second terminal.
5. The method of claim 4, wherein initiating the transition of the pitch
control system comprises opening a contactor operably coupling the pitch motor to a
power converter of the pitch control system, wherein opening the contactor provides a
signal to close the unidirectional switch.
6. The method of claims 4-5, wherein the unidirectional switch comprises
an electro-mechanical switch.
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7. The method of claims 4-5, wherein the unidirectional switch comprises
an electronic switch.
8. The method of claim 7, wherein the electronic switch comprises a
silicone controlled rectifier operably coupled to a gate driver circuit.
9. The method of claims 5-7, further comprising:
completing the transition of the pitch control system from the first operational
mode to the emergency operational mode by operably coupling the pitch motor to the
alternate energy store.
10. The method of claims 1-9, wherein establishing the short-circuit across
the armature of the pitch motor further comprises:
operably coupling a first lead of a unidirectional switch to the first terminal of
the pitch motor; and
operably coupling a second lead of the unidirectional switch to a series field of
the pitch motor, wherein coupling to the series field establishes a variable braking
torque which increases with a torque resulting from the rotation of the rotor blade.
11. A pitch control system for applying a pitch motor braking torque to a
rotor blade of a wind turbine, the pitch control system comprising:
a pitch motor operably coupled to the rotor blade of the wind turbine, the pitch
motor having an absence of supply current during a transition from a first operational
mode of the pitch control system to an emergency operational mode of the pitch
control system;
a first coupling between the pitch motor and a pitch power converter when the
pitch control system is in the first operational mode, wherein opening the first
coupling initiates a transition of the pitch control system from the first operational
mode to the emergency operational mode;
a short-circuit across an armature of the pitch motor, wherein the short-circuit
establishes a current flow between a first terminal and a second terminal of the pitch
motor, wherein the current flow is generated by the pitch motor in response to a
rotation of the rotor blade about the pitch axis when the pitch motor the absence of
supply current, wherein the pitch motor is configured to generate a braking torque in a
single direction in response to the current generated by the rotation of the rotor blade,
21
the braking torque permitting the rotor blade to move freely to a lesser loaded
orientation to protect the rotor blade from damage; and
a second coupling between the pitch motor and an alternate energy store when
the pitch motor is in the emergency operational mode.
12. The system of claim 11, wherein the short-circuit further comprises a
unidirectional switch operably coupled between the first terminal and the second
terminal of the pitch motor, the unidirectional switch blocking a current flow path
from the first terminal to the second terminal.
13. The system of claim 12, wherein the unidirectional switch comprises
an electronic switch.
14. The system of claim 13, wherein the electronic switch comprises a
silicone controlled rectifier operably coupled to a gate driver circuit, and wherein the
first coupling is a first contactor operably coupling the silicone controlled rectifier to
the alternate energy store upon the initiation of the transition of the pitch control
system from the first operational mode to the emergency operational mode.
15. The system of claims 11-14, wherein the rotation of the rotor blade is a
pitch-to-power rotation, wherein the braking torque resists the pitch-to-power
rotation, and wherein the movement to a lesser loaded orientation is a pitch-to-feather
rotation of the rotor blade.