System and method for applying pitch motor braking torque to wind turbine rotor blades

Abstract

A system and method for applying a pitch motor braking torque to a rotor blade is provided. Accordingly, a transition of a pitch control system from a first operating mode to an emergency operating mode is initiated. The pitch motor of the pitch control system has no supply current during the transition. A short circuit is established across the armature of the pitch motor to establish current flow. When the pitch motor has no supply current, current is generated by the pitch motor in response to rotation of the rotor blade about a pitch axis. In response to the generated current flow, a braking torque in a single direction is generated by the pitch motor to allow the rotor blade to freely move to a less loaded orientation relative to the original orientation to protect the wind turbine from damage.

Description

Technical Field

[0001] The present disclosure relates generally to wind turbines, and more particularly to systems and methods for applying pitch motor braking torque to rotor blades of a wind turbine. Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have gained increasing 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 the generator. The rotor assembly and the gearbox are mounted on a bedplate support frame located within the nacelle. One or more rotor blades use the known airfoil principle to capture the kinetic energy of the wind. The rotor blades transmit kinetic energy in the form of rotational energy to rotate a shaft that couples the rotor blades to the gearbox (or directly to the generator if a gearbox is not used). The generator then converts the mechanical energy into electrical energy, and the electrical energy can be transmitted to a converter and / or transformer housed in the tower and subsequently deployed to the utility grid. A modern wind power generation system typically takes the form of a wind farm having a plurality of such wind turbine generators that are operable to supply power to a transmission system that provides power to the power grid.

[0003] Typically, the rotor blades are rotated, or pitched, about the pitch axis via a pitch control system, which is driven by a pitch motor 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 alternative energy source. During the transition from the pitch power converter to the alternative energy source, there may be periods during which no torque is applied by the pitch motor. Consequently, gravity and / or inertia may cause the rotor blades to rotate uncontrollably in the direction of an undesired load. This, in turn, may lead to an overload condition on the rotor blades, resulting in component and / or wind turbine failure.

[0004] In addition to overload conditions, uncontrolled rotation of rotor blades in an undesirable load direction can also cause the pitch motor to generate current. This current can flow to the alternative energy source and interfere with the pitch control system being powered by the alternative energy source. Therefore, it may be desirable to control the rotation of the rotor blades during the transition between the pitch power converter and the alternative energy source.

[0005] Therefore, the art is continually seeking new and improved systems for limiting uncontrolled rotation of rotor blades in an undesirable load direction during a transition to an alternative energy source. Accordingly, the present disclosure is directed to systems and methods for applying pitch motor braking torque to rotor blades. Summary of the Invention

[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 relates 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 blades for rotating the rotor blades about a pitch axis. The method may include initiating a transition of the pitch control system from a first operating mode to an emergency operating mode. The pitch motor of the pitch control system may not have a 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. When the pitch motor does not have a supply current, a current flow may be generated by the pitch motor in response to rotation of the rotor blades about the pitch axis. In response to the generated current flow, the method may also include generating a braking torque in a single direction with the pitch motor so as to allow the rotor blades to move freely to a less loaded direction to protect the turbine from damage.

[0008] In an embodiment, the rotation of the rotor blades is a pitch to power rotation.

[0009] In additional embodiments, generating a braking torque in a single direction may resist rotation of the rotor blades to provide power, and movement to a less loaded orientation may include rotation of the rotor blades to feather.

[0010] In an embodiment, establishing the short circuit across the armature of the pitch motor may further include blocking a current flow path from the first terminal to the second terminal via a one-way switch.

[0011] In additional embodiments, initiating a transition of the pitch control system may include opening a contactor that operably couples the pitch motor to a power converter of the pitch control system. Opening the contactor may also initiate power flow from the alternative energy source to the one-way switch.

[0012] In further embodiments, the one-way switch may be an electromechanical switch.

[0013] In an embodiment, the unidirectional switch may be an electronic switch. In such an embodiment, for example, the electronic switch may include a silicide controlled rectifier operably coupled to a gate driver circuit.

[0014] In an embodiment, the method may further include transitioning the pitch control system from the first operating mode to the emergency operating mode by operatively coupling the pitch motor to an alternative energy source.

[0015] In an embodiment, establishing a short circuit across the armature of the pitch motor may further include operatively coupling a first lead of a one-way switch to a first terminal of the pitch motor. The method may further include operatively coupling a second lead of the one-way switch to a series field of the pitch motor. Coupling to the series field may establish a variable braking torque that increases with torque generated by rotation of the rotor blades.

[0016] In another aspect, the present disclosure relates to a system for applying a pitch braking torque to rotor blades of a wind turbine via a pitch control system. The pitch control system may include a pitch motor operably coupled to the pitch control system of the wind turbine's rotor blades. During a transition from a first operating mode of the pitch control system to an emergency operating mode of the pitch control system, the pitch motor may be deprived of supply current. 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 operating mode. Disconnecting the first coupling may initiate the transition of the pitch control system from the first operating mode to the emergency operating mode. The system may also include a second coupling between the pitch motor and an alternative energy source when the pitch motor is in the emergency operating mode. Additionally, the system may include a short circuit across an armature of the pitch motor. The short circuit may establish current flow between a first terminal and a second terminal of the pitch motor. When the pitch motor is deprived of supply current, current flow may be generated by the pitch motor in response to rotation of the rotor blades about a pitch axis. 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 blades. The braking torque may allow the rotor blade to move freely toward a less loaded orientation to protect the rotor blade from damage.It should be understood that the system may also include any of the additional features described herein.

[0017] In another aspect, the present disclosure relates to a method for applying a unidirectional pitch motor braking torque to rotor blades of a wind turbine. The wind turbine may have a pitch control system operably coupled to the rotor blades for rotating the rotor blades about a pitch axis. The method may include rotating the rotor blades about the pitch axis in a pitch-to-power manner. 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 operating mode to an emergency operating mode. Additionally, the method may include establishing a unidirectional short circuit across an armature of the pitch motor. The method may also include generating current via the pitch motor in response to the rotation of the rotor blades for pitching for power. The current generated by the pitch motor may flow back to the pitch motor via the short circuit. In response to the current generated by the rotation of the rotor blades for pitching for power, the method may also include generating a braking torque in a single direction with the pitch motor. The braking torque may resist the rotation of the rotor blades for pitching for power and allow the rotation of the rotor blades for pitching for feathering. It should be understood that the method may also include any of the additional features and / or steps described herein.

[0018] Technical Solution 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 operatively coupled to the rotor blade for rotating the rotor blade about a pitch axis, the method comprising:

[0019] initiating a transition of the pitch control system from a first operating mode to an emergency operating mode, a pitch motor of the pitch control system having no supply current during the transition;

[0020] establishing a short circuit across an armature of the pitch motor 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 rotation of the rotor blade about the pitch axis when the pitch motor has no supply current; and

[0021] In response to the generated current flow, a braking torque in a single direction is generated with the pitch motor to allow the rotor blade to freely move to a less loaded orientation relative to an original orientation to protect the rotor blade from damage.

[0022] Technical Solution 2. The method according to Technical Solution 1, wherein the rotation of the rotor blades is a rotation in which pitch is varied to provide power.

[0023] Technical Solution 3. The method according to Technical Solution 2, wherein the braking torque in the single direction is generated to resist the rotation of the rotor blades to provide power, and wherein the movement to the direction with less load includes the rotation of the rotor blades to provide power.

[0024] Technical Solution 4. The method according to Technical Solution 3, wherein establishing the short circuit across the armature of the pitch motor further comprises blocking a current flow path from the first terminal to the second terminal via a one-way switch.

[0025] Technical Solution 5. A method according to Technical Solution 4, wherein initiating the transition of the pitch control system includes disconnecting a contactor that operably connects the pitch motor to a power converter of the pitch control system, wherein disconnecting the contactor provides a signal to close the one-way switch.

[0026] Technical Solution 6. The method according to Technical Solution 4, wherein the one-way switch comprises an electromechanical switch.

[0027] Technical Solution 7. The method according to Technical Solution 4, wherein the one-way switch comprises an electronic switch.

[0028] Technical Solution 8. The method according to Technical Solution 7, wherein the electronic switch comprises a silicide controlled rectifier operably coupled to a gate driver circuit.

[0029] Technical Solution 9. The method according to Technical Solution 5, wherein the method further comprises:

[0030] Transitioning the pitch control system from the first operating mode to the emergency operating mode is accomplished by operatively coupling the pitch motor to alternative energy storage.

[0031] Technical Solution 10. The method according to Technical Solution 1, wherein establishing the short circuit across the armature of the pitch motor further comprises:

[0032] operably coupling a first lead of a one-way switch to a first terminal of the pitch motor; and

[0033] A second leg of the one-way switch is operably coupled to a series field of the pitch motor, wherein coupling to the series field establishes a variable braking torque that increases with torque generated by rotation of the rotor blades.

[0034] Technical Solution 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:

[0035] a pitch motor operatively coupled to a rotor blade of the wind turbine, the pitch motor having no supply current during a transition from a first operating mode of the pitch control system to an emergency operating mode of the pitch control system;

[0036] a first coupling between the pitch motor and the pitch power converter when the pitch control system is in the first operating mode, wherein opening the first coupling initiates a transition of the pitch control system from the first operating mode to the emergency operating mode;

[0037] 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 rotation of the rotor blade about the pitch axis when the pitch motor has no 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 allowing the rotor blade to move freely toward a less loaded orientation to protect the rotor blade from damage; and

[0038] A second coupling is provided between the pitch motor and an alternative energy storage when the pitch motor is in the emergency operating mode.

[0039] Technical Solution 12. The system according to Technical Solution 11, wherein the short circuit further comprises a one-way switch, the one-way switch being operably connected between the first terminal and the second terminal of the pitch motor, the one-way switch blocking the current flow path from the first terminal to the second terminal.

[0040] Technical Solution 13. A system according to Technical Solution 12, wherein the one-way switch comprises an electronic switch.

[0041] Technical Solution 14. The system according to Technical Solution 13, wherein the electronic switch comprises a silicide controlled rectifier operably connected to a gate driver circuit.

[0042] Technical Solution 15. A system according to Technical Solution 14, wherein the first connecting member is a first contactor, and when the pitch control system initiates the transition from the first operating mode to the emergency operating mode, the first contactor operably connects the silicide controlled rectifier to the alternative energy storage.

[0043] Technical Solution 16. A system according to Technical Solution 11, wherein the rotation of the rotor blades is a rotation of pitching to provide power, wherein the braking torque resists the rotation of pitching to provide power, and wherein the movement to a direction with less load is a rotation of the rotor blades of pitching to provide power.

[0044] Technical Solution 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 operatively coupled to the rotor blade for rotating the rotor blade about a pitch axis, the method comprising:

[0045] rotating the rotor blades about the pitch axis in a manner to pitch to provide power;

[0046] opening a contactor operatively 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 operating mode to an emergency operating mode;

[0047] establishing a unidirectional short circuit across the armature of the pitch motor;

[0048] generating current via the pitch motor in response to pitching the rotor blades to provide rotation of the power, wherein the current generated by the pitch motor flows back to the pitch motor via the short circuit; and

[0049] A braking torque in a single direction is generated with the pitch motor in response to current generated by the pitch-to-power rotation of the rotor blades, wherein the braking torque resists the pitch-to-power rotation of the rotor blades and allows the pitch-to-feather rotation of the rotor blades.

[0050] Technical Solution 18. The method according to Technical Solution 17, wherein establishing the short circuit further comprises:

[0051] A one-way switch is triggered, the one-way switch being operably coupled between a first terminal and a second terminal of the pitch motor, the one-way switch blocking a current flow path from the first terminal to the second terminal.

[0052] Technical Solution 19. The method according to Technical Solution 18, wherein the unidirectional switch comprises a silicide controlled rectifier operably coupled to a gate driver circuit.

[0053] Technical Solution 20. The method according to Technical Solution 19, wherein opening the contactor allows the silicide controlled rectifier to be operably connected to an alternative energy storage.

[0054] 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 present invention and, together with the description, serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] A complete and enabling disclosure of the invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0056] Figure 1 A perspective view illustrating one embodiment of a wind turbine according to the present disclosure;

[0057] Figure 2 A perspective interior view showing one embodiment of a nacelle of a wind turbine according to the present disclosure;

[0058] Figure 3 A circuit diagram illustrating one embodiment of a pitch control system according to the present disclosure;

[0059] Figure 4 A circuit diagram illustrating one embodiment of a pitch control system according to the present disclosure;

[0060] Figure 5 a flow chart illustrating one embodiment of a method for applying pitch motor braking torque to rotor blades of a wind turbine according to the present disclosure; and

[0061] Figure 6 A flow chart illustrating one embodiment of a method for applying unidirectional pitch motor braking torque to rotor blades of a wind turbine according to the present disclosure.

[0062] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. DETAILED DESCRIPTION

[0063] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the drawings. Each example is provided as an explanation of the present invention and is not a limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, features shown or described as part of one embodiment may be used in another embodiment to generate further embodiments. Therefore, it is intended that the present invention covers such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0064] As used herein, the terms “first,” “second,” and “third” are used interchangeably to distinguish one component from another and are not intended to indicate the position or importance of each component.

[0065] Unless otherwise specified herein, the terms "coupled," "fixed," "attached," and the like refer to both direct coupling, fixing, or attachment as well as indirect coupling, fixing, or attachment through one or more intermediate members or features.

[0066] As used herein throughout the specification and claims, approximating language is used to modify any quantitative representation that is permissible to vary without resulting in a change in the basic function to which it relates. Accordingly, values ​​modified by one or more terms such as "about," "approximately," and "substantially" are not limited to the precise values ​​specified. In at least some cases, approximate language may correspond to the precision of an instrument used to measure a value, or the precision of a method or machine used to construct or manufacture a component and / or system. For example, approximate language may refer to within a 10 percent margin.

[0067] Here and throughout the specification and claims, range limitations are combined and interchangeable, and unless context or language indicates otherwise, such ranges are identified and include all subranges contained therein. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

[0068] In general, the present disclosure relates to systems and methods for applying a pitch motor braking torque to rotor blades of a wind turbine. In particular, the present disclosure includes a system and method for resisting rotation of rotor blades in an undesired load direction when a pitch motor of a pitch control system is not powered. In particular, the present disclosure may include initiating a transition of the pitch control system from a first operating mode to an emergency operating mode. The transition may include switching a power source for the pitch control system from a pitch power converter to an alternative energy source. During the transition, no current may flow from an external source to the pitch motor, and the pitch motor may be unable to generate torque to control rotation of the rotor blades about a pitch axis. Thus, a short circuit may be established across the armature of the pitch motor. The short circuit may allow current generated by the unpowered motor in response to uncontrolled rotation of the rotor blades 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. Braking torque can resist rotation of the rotor blades in an undesirable load direction (e.g., pitching to provide power) while allowing rotation in a less loaded direction (e.g., pitching to feather). Resisting rotation in a more loaded direction can protect the rotor blades and wind turbine from damage due to overload.

[0069] Now refer to the figure, Figure 1A perspective view of one embodiment of a wind turbine 100 according to the present disclosure is shown. As shown, wind turbine 100 generally includes a tower 102 extending from a support surface 104, a nacelle 106 mounted on tower 102, and a rotor 108 coupled to nacelle 106. Rotor 108 includes a rotatable hub 110 and at least one rotor blade 112 coupled to hub 110 and extending outwardly from hub 110. For example, in the illustrated embodiment, rotor 108 includes three rotor blades 112. However, in alternative embodiments, rotor 108 may include more or less than three rotor blades 112. Each rotor blade 112 may be spaced about hub 110 to facilitate rotating rotor 108 so that kinetic energy can be converted from the wind into usable mechanical energy and subsequently into electrical energy. For example, hub 110 may be rotatably coupled to a generator 118 ( Figure 2 ), to allow the generation of electrical energy.

[0070] Now refer to Figure 2 , showing Figure 1 , a simplified internal diagram of one embodiment of a nacelle 106 of a wind turbine 100 is shown in FIG. As shown, a generator 118 may be coupled to the rotor 108 for generating electrical power from the 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 main bearings 144. The rotor shaft 122 may, in turn, be rotatably coupled to a high-speed shaft 124 of the generator 118 via a gearbox 126, which is connected to a bedplate support frame 136 by one or more torque arms 142. As generally understood, the rotor shaft 122 may provide a low-speed, high-torque input to the gearbox 126 in response to the 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 into a high-speed, low-torque output to drive the high-speed shaft 124 and, therefore, the generator 118.

[0071] Now refer to Figure 2-4In an embodiment, each rotor blade 112 may further include a pitch control system 120 configured to rotate each rotor blade 112 about its pitch axis 116. Each pitch control system 120 may further include a pitch motor 128, a pitch drive gearbox 130, and a pitch drive pinion 132. In such an embodiment, the pitch motor 128 may be coupled to the pitch drive gearbox 130 such that the pitch motor 128 imparts mechanical force to the pitch drive gearbox 130. Similarly, the pitch drive gearbox 130 may be coupled to the pitch drive pinion 132 for rotation therewith. The pitch drive pinion 132, in turn, may be in rotational engagement with a pitch bearing 134 coupled between the hub 110 and the corresponding rotor blade 112 such that rotation of the pitch drive pinion 132 causes rotation of the pitch bearing 134. Thus, in such embodiments, rotation of pitch motor 128 drives pitch drive gearbox 130 and pitch drive pinion 132 , thereby rotating pitch bearing 134 and rotor blade 112 about pitch axis 116 .

[0072] In an embodiment, Figure 3 and Figure 4 As particularly shown in FIG, pitch motor 128 may be operably coupled to pitch power converter 146. In at least one embodiment, the coupling between pitch motor 128 and pitch power converter 146 may be a first coupling 148. In embodiments, first coupling 148 may be a contactor, a relay, a switch, a manual controller, or any other device suitable for switching electrical power. When pitch control system 120 is in at least a first operating mode, pitch power converter 146 delivers supply current to pitch motor 128.

[0073] In additional embodiments, as shown, pitch motor 128 can be operably coupled to alternative energy source 150. In at least one embodiment, the coupling between pitch motor 128 and alternative energy source 150 can be a second coupling 152. In embodiments, second coupling 152 can be a contactor, a relay, a switch, a manual controller, or any other device suitable for switching electrical power. Alternative energy source 150 can be a battery bank, a capacitor bank, a backup generator, and / or other power source suitable for providing supply current to pitch motor 128 during periods when supply current from pitch power converter 146 is unavailable. Thus, when pitch control system 120 is in the emergency operating mode, alternative energy source 150 delivers supply current to pitch motor 128.

[0074] In at least one embodiment, pitch control system 120 may transition from the first operating mode to the emergency mode in response to a fault associated with the supply current delivered by pitch power converter 146. In other words, in an embodiment, the fault may exist within pitch power converter 146 or within a power grid coupled to pitch power converter 146 (which may require a transition to the emergency mode). The transition may be initiated by disconnecting first coupling 148. During the transition from the first operating mode to the emergency operating mode, pitch motor 128 may be without supply current when first coupling 148 is disconnected from pitch power converter 146. In at least one embodiment, pitch motor 128 may be without supply current for greater than or equal to 50 milliseconds (ms) (e.g., greater than or equal to 100 ms). In additional embodiments, pitch motor 128 may be without supply current for less than or equal to 500 ms (e.g., less than or equal to 300 ms). In an embodiment, transitioning pitch control system 120 from the first operating mode to the emergency operating mode may be accomplished by operatively coupling pitch motor 128 to alternative energy source 150 via second coupling 152 .

[0075] It should be appreciated that a delay in the transition from the first operating mode to the emergency operating mode may result in a period during which no torque is generated by pitch motor 128. Without torque provided by pitch motor 128, rotor blades 112 may be free to rotate in an uncontrolled manner in response to inertia and / or external forces (e.g., gravity or wind). For example, in embodiments where rotor blades 112 may rotate about pitch axis 116 before disconnecting first coupling 148, rotor blades 112 may continue to rotate due to inertia. In at least one embodiment, this rotation may be in a direction where aerodynamic loads are greater (e.g., pitching to provide power).

[0076] Still refer to Figure 3 and Figure 4 In an embodiment, pitch motor 128 may be a brushed DC motor having two field windings. One of the field windings may be a shunt field winding 156 that is energized independently of armature 154 of pitch motor 128. The other of the field windings may be a series field winding 158. Series field winding 158 may be energized by current flowing through armature 154. The energization of series field winding 158 may be a result of supplied current or may be a result of current generated by pitch motor 128 in response to uncontrolled (e.g., unintended) rotation of rotor blades 112 about pitch axis 116.

[0077] like Figure 3 and Figure 41 , pitch control system 120 may further include a short circuit 160 across armature 154 of pitch motor 128. Short circuit 160 may establish a current flow between a first terminal 162 and a second terminal 164 of pitch motor 128. The current flow may be generated by pitch motor 128 in response to rotation of rotor blade 112 about pitch axis 116. In an embodiment, pitch motor 128 may be configured to generate a braking torque in a single direction in response to the current generated by the rotation of rotor blade 112. The braking torque may allow rotor blade 112 to freely move toward a less loaded orientation to protect rotor blade 112 from damage.

[0078] In an embodiment, pitch control system 120 may include a one-way switch 166 as a component of short circuit 160. One-way switch 166 may be operably coupled between first terminal 162 and second terminal 164 of pitch motor 128. One-way switch 166 may block current flow from first terminal 162 to second terminal 164, while allowing current flow from second terminal 164 to first terminal 162. In an embodiment, the blocked current flow from first terminal 162 to second terminal 164 may be generated by pitch motor 128 in response to rotation of rotor blades 112 toward a less loaded orientation (e.g., pitching to feather). In additional embodiments, the allowed current flow from second terminal 164 through one-way switch 166 to first terminal 162 may be generated by pitch motor 128 in response to rotation of rotor blades 112 toward a more loaded orientation. It should be appreciated that the flow of current from second terminal 164 to first terminal 162 may cause pitch motor 128 to generate a pitch motor braking torque in a single direction while allowing rotor blade 112 to freely move toward a less loaded orientation. In other words, in at least one embodiment, uncontrolled pitching of rotor blade 112 to provide power may generate a current in one coil of pitch motor 128, which in turn is used by another coil of pitch motor 128 to generate a pitch motor braking torque to resist the pitching of rotor blade 112 to provide power.

[0079] In at least one embodiment, one-way switch 166 may include an electronic switch. The electronic switch may include a silicide controlled rectifier 168 operably coupled to gate driver circuit 170. In at least one embodiment, disconnecting first coupling 148 upon initiating a transition of pitch control system 120 from the first operating mode to the emergency operating mode may initiate power flow from alternative energy source 150 through first coupling 148 and to one-way switch 166. In other words, while pitch motor 128 is disconnected from pitch power converter 146, one-way switch 166 may be coupled to and powered by alternative energy source 150. It should be appreciated that, in at least one embodiment, one-way switch 166 may be an electromechanical switch.

[0080] like Figure 4 , in an embodiment, establishing short circuit 160 across armature 154 of pitch motor 128 may include operatively coupling first lead 172 of one-way switch 166 to first terminal 162 of pitch motor 128, and operatively coupling second lead 174 of one-way switch 166 to series field 158 of pitch motor 128. It should be appreciated that coupling one-way switch 166 to series field 158 may cause series field 158 to be incorporated into short circuit 160. It should also be appreciated that coupling series field 158 into short circuit 160 may establish a variable braking torque that increases with the torque generated by the rotation of rotor blades 112.

[0081] Now refer to Figure 5 , a flow chart illustrating one embodiment of a method 200 for applying a pitch motor braking torque to a rotor blade of a wind turbine. For example, the method 200 may be implemented using the method described above with reference to Figure 1-4 For purposes of illustration and discussion, the pitch control system 120 of the present disclosure is implemented. Figure 5 The steps are depicted as being performed in a particular order. Using the disclosure provided herein, one of ordinary skill in the art will understand that the various steps of method 200, or any of the methods disclosed herein, may be adjusted, modified, rearranged, performed simultaneously, or modified in various ways without departing from the scope of the present disclosure.

[0082] As shown at (202), method 200 may include initiating a transition of the pitch control system from a first operating mode to an emergency operating mode. A pitch motor of the pitch control system may not have a supply current during the transition. As shown at (204), method 200 may include establishing a short circuit across an armature of the pitch motor 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 rotation of the rotor blade about the pitch axis. In response to the generated current flow, as shown at (206), method 200 may include generating a braking torque in a single direction with the pitch motor to allow the rotor blade to move freely to a less loaded direction to protect the rotor blade from damage.

[0083] Now refer to Figure 6 , a flow chart showing another embodiment of a method 300 for applying a unidirectional pitch motor braking torque to a rotor blade of a wind turbine. For example, the method 300 may be performed using the method described above with reference to Figure 1-4 For purposes of illustration and discussion, the pitch control system 120 of the present disclosure is implemented. Figure 6The steps are depicted as being performed in a particular order. Using the disclosure provided herein, one of ordinary skill in the art will understand that the various steps of method 300, or any of the methods disclosed herein, may be adjusted, modified, rearranged, performed simultaneously, or modified in various ways without departing from the scope of the present disclosure.

[0084] As shown at (302), method 300 may include rotating the rotor blades about a pitch axis in a pitch-to-power manner. As shown at (304), method 300 may include disconnecting a contactor operably coupling a pitch motor of a pitch control system to a pitch power converter to initiate a transition of the pitch control mechanism from a first operating mode to an emergency operating mode. As shown at (306), method 300 may include establishing a unidirectional short circuit across an armature of the pitch motor. As shown at (308), method 300 may include generating a current via the pitch motor in response to the rotation of the rotor blades for pitching to power. The current generated by the pitch motor may flow back to the pitch motor via the short circuit. In response to the current generated by the rotation of the rotor blades for pitching to power, as shown at (310), method 300 may include generating a braking torque in a single direction with the pitch motor. The braking torque resists the rotation of the rotor blades for pitching to power and allows the rotation of the rotor blades for pitching to feather.

[0085] In addition, the technical staff will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described and other known equivalents for each such method and feature can be mixed and matched by those of ordinary skill in the art to construct additional systems and techniques according to the principles of this disclosure. Of course, it will be understood that not all such goals or advantages described above may be realized according to any particular embodiment. Therefore, for example, it will be appreciated by those skilled in the art that the systems and techniques described herein may be embodied or performed in a manner that realizes or optimizes an advantage or group of advantages as taught herein, and may not necessarily realize other goals or advantages as taught or suggested herein.

[0086] 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 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 language of the claims.

[0087] Further aspects of the invention are provided by the subject matter of the following clauses:

[0088] Item 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 operating mode to an emergency operating mode, the pitch motor of the pitch control system having no 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 rotation of the rotor blade about the pitch axis when the pitch motor has no supply current; and generating a braking torque in a single direction with the pitch motor in response to the generated current flow so as to allow the rotor blade to move freely to a less loaded orientation relative to an original orientation to protect the rotor blade from damage.

[0089] Clause 2. The method of any preceding clause, wherein the rotation of the rotor blades is rotation that is pitched to provide power.

[0090] Clause 3. The method of any preceding clause, wherein generating the braking torque in a single direction resists pitching of the rotor blades to provide power, and wherein the movement to the less loaded orientation comprises pitching of the rotor blades to feather rotation.

[0091] Clause 4. The method of any preceding clause, wherein establishing a short circuit across the armature of the pitch motor further comprises blocking a current flow path from the first terminal to the second terminal via a one-way switch.

[0092] Clause 5. The method of any preceding clause, wherein initiating transition of the pitch control system comprises opening a contactor operatively coupling the pitch motor to a power converter of the pitch control system, wherein opening the contactor provides a signal to close the one-way switch.

[0093] Clause 6. The method of any preceding clause, wherein the one-way switch comprises an electromechanical switch.

[0094] Clause 7. The method of any preceding clause, wherein the one-way switch comprises an electronic switch.

[0095] Clause 8. The method of any preceding clause, wherein the electronic switch comprises a silicide controlled rectifier operably coupled to the gate driver circuit.

[0096] Clause 9. The method of any preceding clause, further comprising: completing transitioning the pitch control system from the first operating mode to the emergency operating mode by operatively coupling the pitch motor to an alternative energy storage.

[0097] Clause 10. The method of any preceding clause, wherein establishing a short circuit across the armature of the pitch motor further comprises: operably coupling a first lead of a one-way switch to a first terminal of the pitch motor; and operably coupling a second lead of the one-way switch to a series field of the pitch motor, wherein coupling to the series field establishes a variable braking torque that increases with torque generated by rotation of the rotor blades.

[0098] Item 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 no supply current during a transition from a first operating mode of the pitch control system to an emergency operating 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 operating mode, wherein opening the first coupling initiates a transition of the pitch control system from the first operating mode to the emergency operating mode; a coupling across the pitch motor short-circuiting the armature of the pitch motor, wherein the short-circuiting establishes a current flow between the first terminal and the second terminal of the pitch motor, wherein the current flow is generated by the pitch motor in response to rotation of the rotor blade about the pitch axis when the pitch motor has no 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 allowing the rotor blade to move freely in a less loaded direction to protect the rotor blade from damage; and a second coupling between the pitch motor and an alternative energy storage when the pitch motor is in the emergency operating mode.

[0099] Clause 12. The system of any preceding clause, wherein the short circuit further comprises a one-way switch operably coupled between the first terminal and the second terminal of the pitch motor, the one-way switch blocking a current flow path from the first terminal to the second terminal.

[0100] Clause 13. The system of any preceding clause, wherein the one-way switch comprises an electronic switch.

[0101] Clause 14. The system of any preceding clause, wherein the electronic switch comprises a silicide controlled rectifier operably coupled to the gate driver circuit.

[0102] Clause 15. The system of any preceding clause, wherein the first coupling is a first contactor that operatively couples the silicide controlled rectifier to the alternative energy storage upon initiating a transition of the pitch control system from the first operating mode to the emergency operating mode.

[0103] Clause 16. The system of any preceding clause, wherein the rotation of the rotor blades is pitched to power rotation, wherein the braking torque resists the pitched to power rotation, and wherein the movement to the less loaded orientation is pitched to feather rotation of the rotor blades.

[0104] Item 17. A method for applying a unidirectional pitch motor braking torque to a rotor blade of a 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 manner; 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 operating mode to an emergency operating mode; establishing a unidirectional short circuit across an armature of the pitch motor; generating a current via the pitch motor in response to the pitch-to-power rotation of the rotor blade, wherein the current generated by the pitch motor flows back to the pitch motor via the short circuit; and generating a braking torque in a single direction with the pitch motor in response to the current generated by the pitch-to-power rotation of the rotor blade, wherein the braking torque resists the pitch-to-power rotation of the rotor blade and permits the pitch-to-feather rotation of the rotor blade.

[0105] Clause 18. The method of any preceding clause, wherein establishing the short circuit further comprises: triggering a one-way switch operably coupled between the first terminal and the second terminal of the pitch motor, the one-way switch blocking a current flow path from the first terminal to the second terminal.

[0106] Clause 19. The method of any preceding clause, wherein the unidirectional switch comprises a silicide controlled rectifier operably coupled to the gate driver circuit.

[0107] Clause 20. The method of any preceding clause, wherein opening the contactor operatively couples the silicide controlled rectifier to an alternative energy storage.

Claims

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 operatively 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 operating mode to an emergency operating mode, a pitch motor of the pitch control system having no supply current during the transition; establishing a short circuit across an armature of the pitch motor 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 rotation of the rotor blade about the pitch axis toward a more loaded orientation when the pitch motor has no supply current; as well as In response to the generated current flow, a braking torque in a single direction is generated with the pitch motor to allow the rotor blade to freely move to a less loaded orientation relative to an original orientation to protect the rotor blade from damage.

2. The method according to claim 1, characterized in that The rotation of the rotor blades is pitched to provide power.

3. The method according to claim 2, characterized in that Generating the braking torque in the single direction resists pitching of the rotor blades to provide power, and wherein movement to a less loaded orientation includes pitching of the rotor blades to feather rotation.

4. The method according to claim 3, characterized in that Establishing the short circuit across the armature of the pitch motor further includes blocking a current flow path from the first terminal to the second terminal via a one-way switch.

5. The method according to claim 4, characterized in that Initiating a transition of the pitch control system includes opening a contactor that operably couples the pitch motor to a power converter of the pitch control system, wherein opening the contactor provides a signal to close the one-way switch.

6. The method according to claim 4, characterized in that The one-way switch comprises an electromechanical switch.

7. The method according to claim 4, characterized in that The one-way switch includes an electronic switch.

8. The method according to claim 7, characterized in that The electronic switch includes a silicide controlled rectifier operably coupled to a gate driver circuit.

9. The method according to claim 5, characterized in that The method further comprises: Transitioning the pitch control system from the first operating mode to the emergency operating mode is accomplished by operatively coupling the pitch motor to alternative energy storage.

10. The method according to claim 1, characterized in that Establishing the short circuit across the armature of the pitch motor further comprises: operably coupling a first lead of a one-way switch to a first terminal of the pitch motor; and A second leg of the one-way switch is operably coupled to a series field of the pitch motor, wherein coupling to the series field establishes a variable braking torque that increases with torque generated by rotation of the rotor blades.

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 operatively coupled to a rotor blade of the wind turbine, the pitch motor having no supply current during a transition from a first operating mode of the pitch control system to an emergency operating mode of the pitch control system; a first coupling between the pitch motor and the pitch power converter when the pitch control system is in the first operating mode, wherein opening the first coupling initiates a transition of the pitch control system from the first operating mode to the emergency operating 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 rotation of the rotor blade about the pitch axis toward a more loaded orientation when the pitch motor has no 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 allowing the rotor blade to freely move toward a less loaded orientation to protect the rotor blade from damage; as well as A second coupling is provided between the pitch motor and an alternative energy storage when the pitch motor is in the emergency operating mode.

12. The system according to claim 11, wherein: The short circuit further includes a one-way switch operably coupled between a first terminal and a second terminal of the pitch motor, the one-way switch blocking a current flow path from the first terminal to the second terminal.

13. The system according to claim 12, wherein: The one-way switch includes an electronic switch.

14. The system according to claim 13, wherein: The electronic switch includes a silicide controlled rectifier operably coupled to a gate driver circuit.

15. The system according to claim 14, wherein: The first coupling is a first contactor that operatively couples the silicide controlled rectifier to the alternative energy storage upon initiating a transition of the pitch control system from the first operating mode to the emergency operating mode.

16. The system according to claim 11, wherein: The rotation of the rotor blades is a pitched to power rotation, wherein the braking torque resists the pitched to power rotation, and wherein the movement to a less loaded orientation is a pitched to feather rotation of the rotor blades.

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 operatively coupled to the rotor blade for rotating the rotor blade about a pitch axis, the method comprising: rotating the rotor blades about the pitch axis in a manner to pitch to provide power; opening a contactor operatively 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 operating mode to an emergency operating mode; establishing a unidirectional short circuit across the armature of the pitch motor; generating current via the pitch motor in response to pitching the rotor blades to provide rotation of the power, wherein the current generated by the pitch motor flows back to the pitch motor via the short circuit; as well as A braking torque in a single direction is generated with the pitch motor in response to current generated by the pitch-to-power rotation of the rotor blades, wherein the braking torque resists the pitch-to-power rotation of the rotor blades and allows the pitch-to-feather rotation of the rotor blades.

18. The method according to claim 17, characterized in that Establishing the short circuit further includes: A one-way switch is triggered, the one-way switch being operably coupled between a first terminal and a second terminal of the pitch motor, the one-way switch blocking a current flow path from the first terminal to the second terminal.

19. The method according to claim 18, characterized in that The unidirectional switch includes a silicide controlled rectifier operably coupled to a gate driver circuit.

20. The method according to claim 19, wherein Opening the contactor operatively couples the silicide controlled rectifier to alternative energy storage.

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