Patent Description:
Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a 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.

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 overloaded condition of the rotor blade, thereby leading to component and/or wind turbine failure.

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.

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. The paper "Analysis of instability of direct powered DC-compound machines in pitch systems of large wind turbines" by <CIT> disclose prior art solutions of wind turbine pitch control in emergency operational mode.

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 toward a more loaded orientation 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.

In an embodiment, the rotation of the rotor blade is a pitch-to-power rotation.

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.

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.

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.

In a further embodiment, the unidirectional switch may be an electro-mechanical switch.

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.

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.

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.

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 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 toward a more loaded orientation 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.

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 steps described herein.

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 of the invention as defined by the appended set of claims.

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 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.

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

Referring now to <FIG>, a simplified, internal view of one embodiment of the nacelle <NUM> of the wind turbine <NUM> shown in <FIG> is illustrated. As shown, 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 be rotatably supported by a main bearing <NUM>. The rotor shaft <NUM> may, in turn, be rotatably coupled to a high-speed shaft <NUM> of the generator <NUM> through a gearbox <NUM> connected to a bedplate support frame <NUM> by one or more torque arms <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 high-speed shaft <NUM> and, thus, the generator <NUM>.

Referring now to <FIG>, in an embodiment, each rotor blade <NUM> may also include a pitch control system <NUM> configured to rotate each rotor blade <NUM> about its pitch axis <NUM>. Each pitch control system <NUM> may also include a pitch motor <NUM>, a pitch drive gearbox <NUM>, and a pitch drive pinion <NUM>. In such embodiments, the pitch motor(s) <NUM> may be coupled to the pitch drive gearbox(s) <NUM> so that the pitch motor(s) <NUM> imparts mechanical force to the pitch drive gearbox(s) <NUM>. Similarly, the pitch drive gearbox(s) <NUM> may be coupled to the pitch drive pinion(s) <NUM> for rotation therewith. The pitch drive pinion(s) <NUM> may, in turn, be in rotational engagement with a pitch bearing <NUM> coupled between the hub <NUM> and a corresponding rotor blade <NUM> such that rotation of the pitch drive pinion(s) <NUM> causes rotation of the pitch bearing(s) <NUM>. Thus, in such embodiments, rotation of the pitch motor(s) <NUM> drives the pitch drive gearbox(s) <NUM> and the pitch drive pinion(s) <NUM>, thereby rotating the pitch bearing(s) <NUM> and the rotor blade(s) <NUM> about the pitch axis <NUM>.

In an embodiment, as shown particularly in <FIG> and <FIG>, the pitch motor(s) <NUM> may be operably coupled to a pitch power converter <NUM>. In at least one embodiment, the coupling between the pitch motor(s) <NUM> and the pitch power converter <NUM> may be a first coupling <NUM>. The first coupling <NUM> 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 <NUM> delivers an supply current to the pitch motor(s) <NUM> when the pitch control system(s) <NUM> is in at least a first operational mode.

In an additional embodiment, as shown, the pitch motor(s) <NUM> may be operably coupled to an alternate energy source <NUM>. In at least one embodiment, the coupling between the pitch motor(s) <NUM> and the alternate energy source <NUM> may be a second coupling <NUM>. The second coupling <NUM> 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 <NUM> 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) <NUM> during an unavailability of the supply current from the pitch power converter <NUM>. As such, the alternate energy source <NUM> delivers an supply current to the pitch motor(s) <NUM> when the pitch control system(s) <NUM> is in an emergency operational mode.

In at least one embodiment, the pitch control system(s) <NUM> 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 <NUM>. In other words, in an embodiment, a failure may reside within the pitch power converter <NUM> 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 <NUM>. As opening the first coupling <NUM> decouples the pitch motor(s) <NUM> from the pitch power converter <NUM>, during the transition from the first operational mode to emergency operational mode, the pitch motor(s) <NUM> may have an absence of supply current. In at least one embodiment, the pitch motor(s) <NUM> may have an absence of supply current for greater than or equal to <NUM> milliseconds (ms) (e.g., greater than or equal to <NUM>). In an additional embodiment, the pitch motor(s) <NUM> may have an absence of supply current for less than or equal to <NUM> (e.g., less than or equal to <NUM>). In an embodiment, the transition of the pitch control system(s) <NUM> from the first operational mode to an emergency operational mode may be completed by operably coupling the pitch motor(s) <NUM> to the alternate energy source <NUM> via the second coupling <NUM>.

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) <NUM>. In the absence of a torque provided by the pitch motor(s) <NUM>, the rotor blade(s) <NUM> may freely rotate in an 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) <NUM> may be rotating about the pitch axis <NUM> prior to the opening of the first coupling <NUM>, the rotor blade(s) <NUM> 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).

Still referring to <FIG> and <FIG>, in an embodiment, the pitch motor(s) <NUM> may be a brushed DC motor having two field windings. One of the field windings may be a shunt field winding <NUM> which is excited independent of an armature <NUM> of the pitch motor <NUM>. The other of the field windings may be a series field winding <NUM>. The series field winding <NUM> may be excited by the current flowing through the armature <NUM>. The excitation of the series field winding <NUM> may be the result of the supply current or may be the result of a current generated by the pitch motor(s) <NUM> in response to an uncontrolled (e.g., unintended) rotation of the rotor blade(s) <NUM> about the pitch axis <NUM>.

As further depicted in <FIG> and <FIG>, the pitch control system(s) <NUM> may also include a short-circuit <NUM> across the armature <NUM> of the pitch motor(s) <NUM>. The short-circuit <NUM> may establish a current flow between a first terminal <NUM> and a second terminal <NUM> of the pitch motor(s) <NUM>. The current flow may be generated by the pitch motor(s) <NUM> in response to a rotation of the rotor blade(s) <NUM> about the pitch axis <NUM>. 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) <NUM>. The braking torque may permit the rotor blade(s) <NUM> to move freely to a lesser loaded orientation in order to protect the rotor blade(s) <NUM> from damage.

In an embodiment, the pitch control system(s) <NUM> may include a unidirectional switch <NUM> as an element of the short-circuit <NUM>. The unidirectional switch <NUM> may be operably coupled between the first terminal <NUM> and the second terminal <NUM> of the pitch motor(s) <NUM>. The unidirectional switch <NUM> may block a current flow path from the first terminal <NUM> to the second terminal <NUM>, while permitting a current flow from the second terminal <NUM> to the first terminal <NUM>. In an embodiment, the blocked current flow from the first terminal <NUM> to the second terminal <NUM> may be generated by the pitch motor(s) <NUM> in response to the rotation of the rotor blade(s) <NUM> toward a lesser loaded orientation (e.g., a pitch-to-feather). The current flow which is allowed to pass through the unidirectional switch <NUM> from the second terminal <NUM> to the first terminal <NUM> is generated by the pitch motor(s) <NUM> in response to a rotation of the rotor blade(s) <NUM> toward a more loaded orientation. It should be appreciated that the current flow from the second terminal <NUM> to the first terminal <NUM> may result in the pitch motor(s) <NUM> generating the pitch motor braking torque in a single direction while allowing the rotor blades <NUM> 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) <NUM> may generate the current in one coil of the pitch motor(s) <NUM> which, in turn, is utilized by the other coil of the pitch motor(s) <NUM> to generate the pitch motor braking torque to resist the pitch-to-power of the rotor blade(s) <NUM>.

In at least one embodiment, the unidirectional switch <NUM> may include an electronic switch. The electronic switch may include a silicone controlled rectifier <NUM> operably coupled to a gate driver circuit <NUM>. In at least one embodiment, opening the first coupling <NUM> upon the initiation of the transition of the pitch control system(s) <NUM> from the first operational mode to the emergency operational mode may initiate a power flow from the alternate energy source <NUM>, through first coupling <NUM>, and to the unidirectional switch <NUM>. In other words, instantaneous with the decoupling of the pitch motor(s) <NUM> from the pitch power converter <NUM>, the unidirectional switch <NUM> may be coupled to, and powered by, the alternate energy source <NUM>. It should be appreciated that in at least one embodiment, the unidirectional switch <NUM> may be an electro-mechanical switch.

As particularly depicted in <FIG>, in an embodiment, establishing the short-circuit <NUM> across the armature <NUM> of the pitch motor(s) <NUM> may include operably coupling a first lead <NUM> of the unidirectional switch <NUM> to the first terminal <NUM> of the pitch motor(s) <NUM>, and operably coupling a second lead <NUM> of the unidirectional switch <NUM><NUM> the series field <NUM> of the pitch motor(s) <NUM>. It should be appreciated that coupling the unidirectional switch <NUM> to the series field <NUM> may incorporate the series field <NUM> into the short-circuit <NUM>. It should be further appreciated that incorporating the series field <NUM> into the short-circuit <NUM> may establish a variable braking torque which increases with a torque resulting from the rotation of the rotor blade(s) <NUM>.

Referring now to <FIG>, a flow diagram of one embodiment of a method <NUM> for applying a pitch motor braking torque to a rotor blade of a wind turbine is illustrated. The method <NUM> may be implemented using, for instance, the pitch control system(s) <NUM> of the present disclosure discussed above with references to <FIG>. <FIG> 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 <NUM>, 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.

As shown at (<NUM>), the method <NUM> 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 (<NUM>), the method <NUM> 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 <NUM> may, as shown at (<NUM>), 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.

Referring now to <FIG>, a flow diagram of another embodiment of a method <NUM> for applying a unidirectional pitch motor braking torque to a rotor blade of a wind turbine is illustrated. The method <NUM> may be implemented using, for instance, the pitch control system(s) <NUM> of the present disclosure discussed above with references to <FIG>. <FIG> 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 <NUM>, 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.

As shown at (<NUM>), the method <NUM> may include rotating the rotor blade about the pitch axis in a pitch-to-power. As shown at (<NUM>), the method <NUM> 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 (<NUM>), the method <NUM> may include establishing a unidirectional short-circuit across an armature of the pitch motor. As shown at (<NUM>), the method <NUM> 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 <NUM> may as shown at (<NUM>), 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.

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.

Claim 1:
A method for applying a pitch motor (<NUM>) braking torque to a rotor blade (<NUM>) of a wind turbine (<NUM>), the wind turbine (<NUM>) having a pitch control system (<NUM>) operably coupled to the rotor blade (<NUM>) for rotating the rotor blade (<NUM>) about a pitch axis (<NUM>), the method comprising:
initiating a transition of the pitch control system (<NUM>) from a first operational mode to an emergency operational mode, a pitch motor (<NUM>) of the pitch control system (<NUM>) having an absence of supply current during the transition;
establishing a short-circuit (<NUM>) across an armature (<NUM>) of the pitch motor (<NUM>) so as to establish a current flow between a first terminal (<NUM>) and a second terminal (<NUM>) of the pitch motor (<NUM>), wherein the current flow is generated by the pitch motor (<NUM>) in response to a rotation of the rotor blade (<NUM>) about the pitch axis (<NUM>) toward a more loaded orientation when the pitch motor (<NUM>) 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 (<NUM>) so as to allow the rotor blade (<NUM>) to move freely to a lesser loaded orientation relative to an original orientation to protect the rotor blade (<NUM>) from damage.