Methods for operating wind turbines and methods for charging auxiliary power sources

Abstract

To provide methods for operating wind turbines and charging one or more auxiliary power sources for providing auxiliary power to one or more of the wind turbines.SOLUTION: A method comprises pitching wind turbine blades to a predetermined idling pitch angle such that a wind turbine generator (42) produces power for charging one or more auxiliary power sources (84) above a predetermined wind speed. The method further comprises keeping a pitch angle of the blades at the idling pitch angle, and charging the auxiliary power sources (84) when a prevailing wind speed reaches or exceeds the predetermined wind speed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to methods of operating wind turbines, and in particular to methods that include charging an auxiliary power source to provide auxiliary power to one or more wind turbines. The present disclosure further relates to wind turbines. [Background technology]

[0002] Today, wind turbines are used to supply electricity to the power grid. This type of wind turbine (wind turbine generator) generally consists of a tower and a rotor positioned on the tower. The rotor, which usually consists of a hub and several blades, rotates under the influence of wind blowing over the blades. This rotation generates torque, which is usually transmitted to a generator through the rotor shaft, either directly ("direct drive" or "gearless") or by use of a gearbox. In this way, the generator generates electricity, which can be supplied to the power grid.

[0003] The wind turbine hub may be rotatably coupled to the front of the nacelle. The wind turbine hub may be connected to a rotor shaft, which may be rotatably mounted to the nacelle using one or more rotor shaft bearings located in a frame within the nacelle. The nacelle is a housing located on the wind turbine tower that may house and protect the gearbox (if present) and generator (if not located outside the nacelle), and, depending on the wind turbine, may also house and protect additional components such as power converters and auxiliary systems.

[0004] Wind turbines typically consist of electrical systems that require power to operate, such as pitch control systems, ventilation and temperature control systems, communication systems, oil pump systems, etc. The power to operate these systems can come from the grid or from the wind turbine generator.

[0005] In the event of a grid loss, i.e., if the wind turbine is prevented from obtaining or supplying power from the grid for any reason, portions of the wind turbine's electrical system may become inoperable. To extend the operation of at least portions of the wind turbine's electrical system when the grid is unavailable, one or more energy storage and / or energy supply devices may be provided. For example, a battery-based system, an uninterruptible power supply (UPS), a supercapacitor, or one or more diesel generators may be provided.

[0006] When one or more wind turbines of a wind farm are disconnected from the power grid, the disconnected wind turbines may be configured to be in so-called island mode. While the wind turbine is in island mode, some associated wind turbine electrical systems, such as communication systems and ventilation systems, may continue to operate as well until the power provided by the auxiliary power source is exhausted.

[0007] While disconnected from the power grid, and to protect the wind turbine from excessive load, the wind turbine typically idles. That is, the wind turbine blades may be positioned in a feathered position, e.g., at about 90° relative to the rotor plane, to rotate slowly, e.g., at 1 RPM. The wind turbine can remain in such island mode until the power grid connection is restored, provided that the amount of auxiliary power available is sufficient for restart.

[0008] To operate critical auxiliary systems for extended periods of time, a large number of power supply / storage devices and / or relatively large energy supply / storage devices may be required. For example, it is known to provide diesel generators or solar panels to provide power for extended periods of time. Furthermore, if the size and / or number of auxiliary power sources is still not sufficient to provide power for, for example, days or weeks, it may be necessary to travel to the wind turbine site to, for example, recharge / refuel the diesel generators. This can be time-consuming and costly, especially for offshore wind farms.

[0009] There may be other scenarios where wind turbines are prevented from drawing power from the grid and / or where the wind turbine's auxiliary power source is at least partially depleted and it would be beneficial to recharge them. For example, if too much power is being fed into the grid (overkill), some wind turbines may be required to reduce or stop feeding energy into the grid. Wind turbines may also be allowed to idle rather than shut down. Depending on the availability of power from the grid to operate the wind turbine's associated electrical systems, it may be necessary to use energy storage devices. Summary of the Invention [Problem to be solved by the invention]

[0010] The present disclosure aims to provide improvements that will allow a sufficient supply of auxiliary power to be available when needed for a longer period of time.

[0011] In one aspect of the disclosure, a method for operating a wind turbine is provided. The wind turbine includes a wind-powered rotor including a plurality of blades and a wind generator. The wind turbine is configured to supply power from the generator to one or more auxiliary power sources in an autonomous mode. The method includes determining whether a predetermined condition for idling operation of the wind turbine is met. If the predetermined condition for idling operation is met, the method pitches the blades to an idle pitch angle so that the wind turbine generator generates power for charging the auxiliary power source during idling above a predetermined wind speed. The method further includes maintaining the blade pitch angle at the idle pitch angle during idling and charging the auxiliary power source when a prevailing wind speed is equal to or greater than the predetermined wind speed.

[0012] According to this aspect, when certain conditions for idling operation are met, the wind turbine is pitched to a predetermined idling pitch angle, and this pitch angle is maintained regardless of the prevailing wind speed. When the prevailing wind speed is equal to or greater than the predetermined wind speed, the rotor rotation speed during idling is fast enough to start charging, so that the auxiliary power source for supplying auxiliary power to one or more wind turbines can be charged. However, when the prevailing wind speed is equal to or less than the predetermined wind speed, the auxiliary power source may not be charged because the rotor rotation speed is not fast enough to enable charging. In this way, fixed-pitch idling operation is provided, which minimizes the use of power to maintain idling operation while simultaneously maintaining the charging of the auxiliary power source and the load on the wind turbine at an acceptable level.

[0013] In this way, the auxiliary power sources can be charged, possibly not immediately, allowing the wind turbine's associated electrical system to continue operating for a longer period of time. Also, the wind turbine can be better positioned to restart when grid and wind conditions allow it. The wind turbine or wind farm can reduce the number and size of auxiliary power sources needed.

[0014] Throughout this disclosure, an idling condition may be understood as a condition that a wind turbine may detect, for example, by measuring one or more parameters such as wind speed, rotor rotational speed, availability of a power grid to obtain energy from, load, vibration, etc., and that serves as a trigger for pitching the wind turbine blades to a predetermined idling pitch angle. In some examples, the idling condition may be associated with an undue risk of damage to the wind turbine. For example, if such an idling condition, sometimes referred to as a dangerous condition, is detected, the wind turbine is configured to pitch its blades to avoid or at least reduce the risk of damage. In other examples, other conditions may be detected that trigger pitching the blades to a predetermined idling pitch angle.

[0015] Throughout this disclosure, an auxiliary power source may refer to a system or device at least partially configured to store electrical energy that can power certain components of a wind turbine, for example, when the power grid is unavailable. At least one or more of a battery (storage battery) or a supercapacitor, such as an uninterruptible power supply (UPS), may be used. Terms such as auxiliary power source, stored energy source, and energy storage device / system may be used interchangeably herein.

[0016] Throughout this disclosure, the pitch angle of a wind turbine blade may be understood as the angle that can be measured in cross section between a reference line and the chord of the blade. The reference line may, in some examples, be substantially parallel to, e.g., included in, the wind turbine rotor plane. Here, the idle pitch angle may be understood as the pitch angle selected for idling operation. According to an embodiment, the idle pitch angle is not 90° or the blade's "feather" position, but when the wind turbine blade is positioned at this angle, the wind turbine generator can supply power to the auxiliary power source when a predetermined wind speed is reached and cannot generate power below the predetermined wind speed. The idle pitch angle may be selected based on the ability to generate power at a specific wind speed. The idle pitch angle may also be selected to prevent damage to the wind turbine in high winds. High wind speeds may refer to wind speeds above the cut-out wind speed, for example, wind speeds greater than 25 m / s, and may particularly refer throughout this disclosure to wind speeds significantly higher than the cut-out wind speed, for example, wind speeds of 50 m / s or greater, 60 m / s or greater, or 70 m / s or greater.

[0017] Thus, the predetermined wind speed may refer to a threshold value above which a wind turbine with its blades at an idle pitch angle can power an auxiliary power source, but below which the wind turbine cannot. An appropriate idle pitch angle may be selected to maximize the range of wind speeds over which one or more auxiliary power sources of the wind turbine are charged and to avoid damaging the wind turbine if the wind speed is too high. In this way, a good balance may be achieved between the time period available to charge one or more stored energy sources of the wind farm or wind turbine and minimizing the risk of damaging the wind turbine when the wind is too strong.

[0018] Throughout this disclosure, a wind turbine may be understood to be in operation ("normal operation") when its rotor is rotating at a sufficient speed to generate power, the grid is available, and the wind turbine's generator is producing and sending power to the grid. In this specification, the term "normal operation" may be used to explicitly refer to such a situation and to explicitly distinguish it from, for example, operation of a wind turbine in an autonomous mode.

[0019] Throughout this disclosure, the term "autonomous mode" may refer to a mode of operation of a wind turbine in which the wind turbine is disconnected from the power grid and the wind turbine is configured to operate independently of the operation of the power grid. In this mode, power may be obtained from an auxiliary power source to keep one or more of the wind turbine's critical electrical systems operational, such as communication systems, temperature and ventilation regulation systems, bearing lubrication systems, controller systems, and navigation lights.

[0020] In this disclosure, when reference is made to the fact that a wind turbine is (electrically) disconnected from the power grid, it may be understood that the wind turbine is not able to supply or obtain power from the power grid.

[0021] In this disclosure, idling may refer to a wind turbine whose rotor is rotating relatively slowly but which is not supplying power to the grid. Thus, the wind turbine may be idling in an autonomous mode. In some examples, an idling wind turbine may be able to charge its auxiliary power system.

[0022] In a further aspect of the present disclosure, a method for operating a wind turbine is provided. The wind turbine includes a rotor including a plurality of blades and a generator. The wind turbine is configured to supply power from the generator to one or more auxiliary power sources in an autonomous operation mode. The method includes pitching the blades to an idle pitch angle and idling the rotor of the wind turbine at a fixed pitch angle corresponding to the idle pitch angle when the generator is in the autonomous operation mode. The method further includes charging the auxiliary power source when a rotor rotational speed during idling is equal to or greater than a rotational speed threshold, and changing the blade pitch angle when predetermined operating conditions are met.

[0023] In yet another aspect of the present disclosure, a wind turbine is provided that includes a control system configured to perform the example methods described herein. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a perspective view of an example of a wind turbine. [Figure 2] FIG. 2 is a simplified internal view of an example nacelle of the wind turbine of FIG. 1. [Figure 3] 1 is a flow chart illustrating an example method of operating a wind turbine. [Figure 4] 4A, 4B and 4C illustrate schematic diagrams of different pitch angles of a wind turbine blade according to one embodiment. [Figure 5] FIG. 1 illustrates a schematic diagram of an example wind turbine connected to a power grid and one or more auxiliary power sources. [Figure 6] 10 is a flow chart illustrating another embodiment of a method for operating a wind turbine. DETAILED DESCRIPTION OF THE INVENTION

[0025] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of illustration only, and not by way of limitation. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Accordingly, it is intended that the present disclosure cover such modifications and variations as come within the scope of the appended claims and their equivalents.

[0026] FIG. 1 is a perspective view of an example wind turbine 10. In this example, wind turbine 10 is a horizontal axis wind turbine generator. Alternatively, wind turbine 10 may be a vertical axis wind turbine generator. In this example, wind turbine 10 includes a tower 15 extending from a support system 14 on ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 coupled to nacelle 16. Rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from hub 20. In the example, rotor 18 has three rotor blades 22. In alternative embodiments, rotor 18 includes more or fewer than three rotor blades 22. Tower 15 may be fabricated from tubular steel to define a cavity (not shown in FIG. 1 ) between support system 14 and nacelle 16. In alternative embodiments, tower 15 is any suitable type of tower having any suitable height. Alternatively, the tower may be a hybrid tower made of concrete sections and tubular steel sections, or the tower may be a partial or complete lattice tower.

[0027] The rotor blades 22 are spaced apart on the hub 20 to rotate the rotor 18 and convert kinetic energy from the wind into usable mechanical energy, and ultimately electrical energy. The rotor blades 22 are mated to the hub 20 by connecting the blade root portions 24 to the hub 20 at a number of load transfer regions 26. The load transfer regions 26 may include hub load transfer regions and blade load transfer regions (neither of which are shown in FIG. 1 ). Loads induced on the rotor blades 22 are transferred to the hub 20 through the load transfer regions 26.

[0028] In examples, rotor blades 22 may have lengths ranging from about 15 meters (m) to about 90 meters (m) or more. Rotor blades 22 may have any suitable length that enables wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include lengths of 20 meters or less, 37 meters, 48.7 meters, 50.2 meters, 52.2 meters, or greater than 91 meters. When wind strikes rotor blades 22 from wind direction 28, rotor 18 is forced to rotate about rotor axis 30. As rotor blades 22 rotate and experience centrifugal forces, various forces and moments act on rotor blades 22. As such, rotor blades 22 may deflect and / or rotate from a neutral, or undeflected, position to a deflected position.

[0029] Additionally, the pitch angle of the rotor blades 22, e.g., the angle that determines the orientation of the rotor blades 22 relative to the wind direction, may be varied by the pitch system 32 to control the load and power generated by the wind turbine 10 by adjusting the angular position of at least one rotor blade 22 relative to the wind vector. A pitch axis 34 of the rotor blade 22 is shown. During operation of the wind turbine 10, the pitch system 32 may vary the pitch angle of the rotor blades 22 to, among other things, decrease the angle of attack of (some of) the rotor blades, thereby facilitating a reduction in rotational speed and / or facilitating stalling of the rotor 18.

[0030] In a preferred embodiment, the blade pitch of each rotor blade 22 is individually controlled by a wind turbine controller 36 or pitch control system 80. Alternatively, the blade pitch of all rotor blades 22 may be simultaneously controlled by these control systems.

[0031] Additionally, in this embodiment, as wind direction 28 changes, nacelle 16 may be yaw rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0032] While in the example, wind turbine controller 36 is shown as centralized within nacelle 16, wind turbine controller 36 may be a distributed control system throughout wind turbine 10, on support system 14, within a wind farm, and / or at a remote control center. Wind turbine controller 36 may include one or more processors configured to perform one or more of the steps of the methods described herein. Additionally, many of the other components described herein include one or more processors. Wind turbine controller 36 may include memory, e.g., one or more memory devices. As used herein, memory may consist of one or more memory elements, including, but not limited to, computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disk™, compact disc-read only memory (CD-ROM), magneto-optical disk (MOD), digital versatile disc (DVD), and / or other suitable memory elements.

[0033] FIG. 2 is an enlarged cross-sectional view of a portion of wind turbine 10. In this embodiment, wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to nacelle 16. More specifically, a hub 20 of rotor 18 is rotatably coupled to a motor-generator 42 disposed within nacelle 16 by a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In this embodiment, main shaft 44 is disposed at least partially coaxially with a longitudinal axis (not shown) of nacelle 16. Rotation of main shaft 44 drives gearbox 46, which then drives high-speed shaft 48, by converting the relatively slow rotational motion of rotor 18 and main shaft 44 into relatively fast rotational motion of high-speed shaft 48. The latter is connected, with the aid of coupling 50, to generator 42 for producing electrical energy. Additionally, a transformer 90 and / or appropriate electronics, switches, and / or inverters may be disposed within the nacelle 16 to convert the electrical energy generated by the generator 42, e.g., having a voltage between 400V and 1000V, into electrical energy having a medium voltage (e.g., 10-35KV). Offshore wind turbines may have a generator voltage of, e.g., 650V to 3500V, and the transformer voltage may be, e.g., 30kV to 70kV. This electrical energy is conducted from the nacelle 16 to the tower 15 via a power cable.

[0034] In some examples, the wind turbine 10 may include one or more shaft sensors 51. The shaft sensors may be configured to monitor at least one of a torque load acting on the main shaft 44 and / or the high-speed shaft 48 and the rotational speed of the shafts 44, 48. In some examples, the wind turbine 10 may include one or more generator sensors 53. The generator sensors may be configured to monitor at least one of a rotational speed of the generator 42 and a generator torque. The shaft sensors 51 and / or the generator sensors 53 may include, for example, one or more torque sensors (e.g., strain gauges or pressure sensors), optical sensors, accelerometers, magnetic sensors, speed sensors, and micro-inertial measurement units (MIMUs).

[0035] The gearbox 46, generator 42, and transformer 90 may be supported by a main support structural frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 by one or more torque arms 103. In a preferred embodiment, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Additionally, the generator 42 may be attached to the main frame 52 by a decoupling support means 54, particularly to prevent vibrations of the generator 42 from being introduced into the main frame 52 and becoming a source of noise emissions.

[0036] Optionally, main frame 52 is configured to carry the entire loads created by the weight of rotor 18 and nacelle 16 components, and by wind and rotational loads, and to introduce these loads into tower 15 of wind turbine 10. Rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and supports 52, as well as any associated fastening, supporting, and securing devices, including, but not limited to, forward support bearing 60 and aft support bearing 62, may be referred to as drivetrain 64.

[0037] In some examples, the wind turbine may be a direct drive wind turbine without a gearbox 46. The generators 42 operate at the same rotational speed as the rotor 18 in direct drive wind turbines. Therefore, they generally have a much larger diameter than the generators used in wind turbines with gearboxes 46 to provide the same amount of power as wind turbines with gearboxes.

[0038] The nacelle 16 may include a yaw drive mechanism 56 that may be used to rotate the nacelle 16, and thereby the rotor 18, about the yaw axis 38 to control the orientation of the rotor blades 22 relative to the wind direction 28.

[0039] To properly position the nacelle 16 with respect to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system, which may include a wind vane and an anemometer. The meteorological measurement system 58 may provide information to the wind turbine controller 36, which may include the wind direction 28 and / or wind speed.

[0040] In this example, pitch system 32 is at least partially disposed within hub 20 as a pitch assembly 66. Pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in FIG. 1 ) to modulate the pitch angle of rotor blade 22 along pitch axis 34. Only one of the three pitch drive systems 68 is shown in FIG. 2 .

[0041] In the illustrative embodiment, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and each rotor blade 22 (shown in FIG. 1 ) to rotate each rotor blade 22 about pitch axis 34. Pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. Pitch drive motor 74 is coupled to pitch drive gearbox 76 to apply a mechanical force to pitch drive gearbox 76. Pitch drive gearbox 76 is coupled to pitch drive pinion 78 such that pitch drive gearbox 76 rotates pitch drive pinion 78. Pitch bearing 72 is coupled to pitch drive pinion 78 such that rotation of pitch drive pinion 78 causes rotation of pitch bearing 72.

[0042] The pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of the rotor blades 22 in response to one or more signals from the wind turbine controller 36. In examples, the pitch drive motor 74 is any suitable motor driven by an electric and / or hydraulic system that enables the pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components, such as, but not limited to, hydraulic cylinders, springs, and / or servo mechanisms. In certain embodiments, the pitch drive motor 74 is driven by the rotational inertia of the hub 20 and / or energy extracted from a stored energy source (not shown) that provides energy to components of the wind turbine 10.

[0043] Pitch assembly 66 may also include one or more pitch control systems 80 for controlling pitch drive systems 68 according to control signals from wind turbine controller 36 for certain priority conditions and / or during rotor 18 overspeed. In an example embodiment, pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to each pitch drive system 68 for controlling pitch drive systems 68 independently from wind turbine controller 36. In an example embodiment, pitch control system 80 is coupled to pitch drive systems 68 and to sensors 70. During normal operation of wind turbine 10, wind turbine controller 36 may control pitch drive systems 68 to adjust the pitch angle of rotor blades 22.

[0044] According to an embodiment, a power generator 84, comprising, for example, a battery and an electrical capacitor, is disposed on or within the hub 20 and is coupled to the sensors 70, the pitch control system 80, and the pitch drive system 68 to provide a source of electrical power to these components. In an example embodiment, the power source 84 provides a continuous source of electrical power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, the power source 84 supplies power to the pitch assembly 66 only during an electrical power loss event of the wind turbine 10. A power loss event may include a loss or dip in the power grid, a malfunction of the electrical system of the wind turbine 10, and / or a failure of the wind turbine controller 36. During a power loss event, the power generator 84 operates to supply power to the pitch assembly 66 so that the pitch assembly 66 can operate during the power loss event.

[0045] In the example, pitch drive system 68, sensor 70, pitch control system 80, cables, and power supply 84 are each disposed within a cavity 86 defined by an inner surface 88 of hub 20. In alternative embodiments, these components may be positioned relative to and directly or indirectly coupled to an outer surface of hub 20.

[0046] As used herein, the term "processor" is not limited to integrated circuits referred to in the art as computers, but refers broadly to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein.

[0047] In one aspect of the disclosure, a method 100 for operating a wind turbine 10 is provided. The wind turbine 10 comprises a wind turbine rotor 18 including a plurality of blades 22 and a wind turbine generator 42 (e.g., as illustrated in Figures 1 and 2). The wind turbine 10 is configured, at least in an autonomous mode, to supply power from the generator 42 to one or more auxiliary power sources 84. The method 100 is illustrated schematically in the flow chart of Figure 3.

[0048] The wind turbine is configured to provide electrical power from the generator 42 to the auxiliary power source at least in an autonomous mode, i.e., in some examples, the wind turbine is also configured to provide electrical power to the auxiliary power source during normal operation.

[0049] The method comprises determining whether a predetermined condition for idling operation of the wind turbine 10 is met, at block 110. The method further comprises, if the predetermined condition for idling operation is met, pitching the blades 22 to an idle pitch angle 25 such that the wind turbine generator 42 generates electrical power for charging the auxiliary power source above a predetermined wind speed, at block 120. The method further comprises maintaining the pitch angle 25 of the blades 22 at the idle pitch angle 25, at block 130, and charging the auxiliary power source 84 when the prevailing wind speed reaches or exceeds the predetermined wind speed, at block 140.

[0050] Thus, for example, upon detection of a particular condition that may endanger all or part of the wind turbine 10, the wind turbine blades 22 are pitched to a predetermined idle pitch angle 25 at which the generator 42 can generate power to charge one or more auxiliary power supplies 84. For example, one or more energy storage sources 84 may be provided within the nacelle 16 and electrically connected to the generator 42. The predetermined idle pitch angle 25 may be selected so that the auxiliary power supplies 84 are charged when the wind speed reaches a certain value (below which the wind speed is not charged). The idle pitch angle 25 of the blades 22 is kept substantially constant. In this way, below a certain wind speed, the wind generator 42 cannot provide power to charge the auxiliary power supplies. That is, at low wind speeds, no power is generated by the generator or the generated power is not suitable for supplying to the auxiliary power supplies. It has been found that a certain low rotor rotational speed is required to generate power with an appropriate waveform and supply it to the auxiliary power supplies (e.g., via an appropriate power converter). However, once the wind speed reaches, for example, exceeds, a certain wind speed, the generator 42 is able to generate power and the auxiliary power supply 84 begins to charge.

[0051] In this way, the number and / or size of energy storage sources, such as batteries, capacitors, UPS or diesel generators, can be reduced compared to wind turbines 10 that are not capable of implementing method 100 .

[0052] The one or more auxiliary power sources 84 may be located in any suitable location relative to the wind turbine 10. In some examples, the one or more energy storage devices 84 may be located within the nacelle 16. In FIG. 2 , the auxiliary power source 84 is shown for the pitch system 32 of the blade 22. It should be understood that such energy storage sources may be located elsewhere in other embodiments, such as within the tower, at or near the base of the tower, in a transition piece, and so forth. It should also be understood that additional energy storage devices 84 may be provided in the embodiment of FIG. 2 or other embodiments. Auxiliary power sources may also be located within a wind farm to be able to power multiple wind turbines 10.

[0053] "Predetermined" may be understood to mean that the idle condition, the idle pitch angle 25, and the threshold wind speed that allows charging of the auxiliary power source are determined or known in advance, for example, before the idle condition is detected and / or before the idle pitch angle must be adopted. "Predetermined" may also be understood to mean that the idle pitch angle and the threshold wind speed are not continuously determined, adapted, adjusted, or specified.

[0054] In some examples, the idle pitch angle 25 may be selected so that charging begins when a certain wind speed is reached. The pitch angle 25 may also be selected so that the wind turbine 10 is not damaged at high wind speeds. A high wind speed may be understood herein as a wind speed exceeding a cutout wind speed, e.g., exceeding 25 m / s, and in particular may be significantly higher than the cutout wind speed. Because the blades 22 are maintained at the predetermined pitch angle 25 regardless of the prevailing wind speed, it is desirable that the pitch angle 25 be selected so as to not damage the wind turbine 10 at high wind speeds, e.g., 30 m / s, 40 m / s, or higher. In this regard, in the method 100, the idle pitch angle 25, once applied, is not actively or passively controlled but is fixed.

[0055] Idling conditions may generally be determined, identified, or known before installing the wind turbine. In some examples, the predetermined wind speed and idle pitch angle may be determined before installing the wind turbine or during installation or commissioning of the wind turbine. In other examples, the predetermined wind speed and idle pitch angle may be determined during normal or autonomous operation of the wind turbine. For example, if an idle condition is detected during normal or autonomous operation, or if an idle condition is known or suspected to be met in a certain time, e.g., several hours or days, a weather forecast may be used to determine the predetermined wind speed and idle pitch angle. Such predetermined wind speed may, in some examples, be received from a remote operation center.

[0056] In some examples, the statistical distribution of wind speeds at a wind turbine site over a period of time may be known. For example, the trends in wind speed at a wind turbine's location over a period of weeks or months may be known. Taking the wind speed distribution into consideration, an appropriate threshold wind speed at which the wind turbine will begin supplying power to one or more auxiliary power sources 84 while idling may be selected. For example, the threshold wind speed may be the most probable wind speed over a period of time. In another example, a minimum wind speed for charging one or more auxiliary power sources 84 at least a certain number of times within a certain period of time, for example, once a week, may be determined from the wind speed distribution. Then, a rotor speed required for the generator 42 to begin generating power when the selected wind speed is reached may be calculated. Finally, a pitch angle of the blades 22 to achieve the calculated rotor speed may be determined. If a certain idle pitch angle is deemed likely to cause damage to the wind turbine in high winds, a different idle pitch angle may be selected instead, for example, after performing a computer simulation using the initially selected idle pitch angle.

[0057] In another example, safety considerations, such as avoiding or reducing excessive wind turbine load during high winds, may be prioritized when selecting a wind speed threshold and corresponding idle pitch angle. Based on the statistical distribution of wind, it may be possible to probabilistically calculate the likelihood of very high wind speeds occurring during, say, a two-week disconnection from the power grid. Based on this probabilistic calculation, a pitch angle may be determined that allows for acceptable load and idling wind speeds even if such high winds occur. This approach may result in a larger pitch angle, which may result in less frequent charging of the auxiliary power source during idle.

[0058] Similar considerations apply when using weather forecasts to determine the desired wind speed and desired idle pitch angle.

[0059] Throughout this disclosure, the pitch angle of a wind turbine blade 22 may be understood, with reference to Figures 4A, 4B, and 4C, as an angle 25 that may be measured in cross section between a reference line 26 and the chord 27 of the blade. The reference line 26, shown as a dotted line in Figures 4A, 4B, and 4C, may be substantially parallel to the rotor plane of the wind turbine 10. Figures 4A, 4B, and 4C schematically show the blade 22 in cross section. The wind, referenced by arrow "TW," may be blowing from left to right in these figures. Because the wind turbine blade 22 rotates in the plane of the rotor 18 and moves downward in this figure, the apparent wind flow, referenced by arrow "AW," is upward. The apparent wind AW is composed of the wind due to the rotation of the blade and the wind blowing axially TW against the blade 22.

[0060] The right side of the profiles shown in Figures 4A, 4B and 4C can be understood as the suction side of the blade, while the left side can be understood as the pressure side of the blade.

[0061] In Figure 4A, the blade is in a reference position at pitch angle 25. In the reference position, the blade chord 27 is substantially parallel to the reference line 26. In Figure 4A, the blade chord 27 and the reference line 26 overlap. Thus, pitch angle 25 may be 0° or a "default pitch angle." The default pitch angle, or "reference position," may be a position that the wind turbine blade 22 maintains over a range of low wind speeds, for example, a range of sub-nominal wind speeds.

[0062] In FIG. 4B, the blades are pitched away from the reference position. Thus, the pitch angle 25 in FIG. 4B is higher (larger) than in FIG. 4A. In FIG. 4C, the pitch angle 25 is even larger relative to the reference position. Increasing the pitch angle 25 generally can slow down the wind turbine rotor, i.e., the wind turbine blades are positioned to generate less lift and more drag to reduce the aerodynamic torque of the wind turbine rotor. Pitching the blades 22 approximately 90° from the reference position can feather the wind turbine, potentially stopping it completely or at least significantly reducing its rotational speed. The feathered position of the blades is the position the blades might be in when the wind turbine is parked, for example, for maintenance.

[0063] In some examples, the idle pitch angle may be between 55° and 80°, specifically between 60° and 75°. A pitch angle 25 in this interval may allow charging of the auxiliary power source already at frequently occurring wind speeds, thus maximizing the period during which charging occurs, and may also avoid damage to the wind turbine at high wind speeds, e.g., above the cutout wind speed. In other examples, other pitch angles 25 may be deemed appropriate and therefore set as the idle pitch angle.

[0064] In some examples, the idle pitch angle may be such that rotor 18 rotates at at least 1.5 RPM, specifically at least 1.8 RPM, and more specifically at least 2 RPM when blades 22 are at the idle pitch angle and the prevailing wind is at a predetermined wind speed. A minimum rotational speed of rotor 18 may be required for generator 43 to begin generating electricity and charging the energy storage device. Such minimum rotational speed may be on the order of 2 rpm, and the predetermined pitch angle may be set to achieve the minimum rotational speed at a particular (predetermined) wind speed.

[0065] In some examples, the idle pitch angle may be such that the predetermined wind speed is at least 8 m / s, specifically at least 10 m / s, and more specifically at least 12 m / s. In some of these examples, the predetermined wind speed may be between 8, 10, or 12 m / s and 20 m / s. Setting a pitch angle that allows charging to begin at wind speeds of at least 8 m / s, for example, between 8 m / s and 20 m / s, may provide a good balance between allowing charging and avoiding damage to the wind turbine in high winds.

[0066] In some examples, determining whether a predetermined condition for idling operation is met may include determining whether an unsafe condition exists. If an unsafe operating condition is determined and the wind turbine does not operate, damage to the wind turbine may occur. To avoid damage, the blades of the wind turbine are pitched to an idle pitch angle.

[0067] One or more hazard indicators may be detected. In some examples, it may be determined whether the prevailing wind speed is greater than or equal to the cutout wind speed. The prevailing wind speed may be determined, for example, by the meteorological measurement system 58, e.g., an anemometer. In some examples, it may be determined whether the speed of the rotor 18 is greater than or equal to a rotor speed maximum threshold. The current value of the rotor speed may be determined, for example, by the shaft sensor 51 or the generator sensor 51. In some examples, it may be determined whether the load on the wind turbine is greater than or equal to a load threshold. The load may include at least one of force, stress, and vibration. The shaft sensor 51 may be used to determine the load on the wind turbine. Different types of sensors located at different wind turbine locations may generally be used as known in the art. If one or more of these hazardous conditions are met, the blades 22 are pitched to an idle pitch angle. The pitching may help avoid damage to the wind turbine while providing an opportunity to charge the wind turbine and / or the wind farm's energy storage system.

[0068] In some examples, determining whether the predetermined condition for idling has been met may include determining whether a condition for reducing or stopping the supply of power to the power grid has been met. This may be, for example, if the power grid is unbalanced and the power grid is receiving too much power, or if there is a high risk of damage to the wind turbine, for example, if the wind turbine rotor 18 is rotating too fast. If this determination is affirmative, in addition to pitching the blades 22 to the idle pitch angle, the method may further include reducing or stopping the supply of power to the power grid.

[0069] Additionally, the method can, in some examples, further include ceasing to obtain power from the power grid. In response, the wind turbine is not only unable to supply power to the power grid, but also able to receive power from the power grid. Throughout this disclosure, when the wind turbine 10 is neither supplying power to nor obtaining power from the power grid, the wind turbine can be said to be (electrically) decoupled from the power grid. Pitching the blades 120 to an idle pitch angle may occur first, after which the wind turbine may be decoupled from the power grid.

[0070] In some examples, determining whether the predetermined condition for idling operation is met may include determining whether the wind turbine 10 is unable to draw power from the power grid. In some examples, a physical connection between the wind turbine and the power grid may be missing, for example, because a busbar or some cables are damaged or broken. In other examples, a physical connection between the wind turbine and the power grid may exist, but the wind turbine may be unable to obtain power from the power grid for other reasons, for example, an electrical fault. In some examples, determining whether the predetermined operating condition is met may include determining whether the wind turbine has lost connection to the power grid, i.e., when the wind turbine is unable to supply power to the power grid in addition to being unable to draw power from the power grid.

[0071] Determining whether a predetermined condition for idling is met may, in some examples, be performed during normal operation of the wind turbine, i.e., while the wind turbine is supplying power to the power grid. For example, the existence of an unsafe condition of the wind turbine and whether the wind turbine is able to supply power to and / or draw power from the power grid may be confirmed during normal operation of the wind turbine.

[0072] If determining step 110 is performed while the wind turbine is in a normal operating mode, the wind turbine 10 may, in some examples, enter an autonomous operating mode. In this mode, the wind turbine's associated electrical systems may be powered by an auxiliary power source to maintain operation. For example, it may be necessary to maintain communication systems, climate control systems, and ventilation systems in an operational state. Because the blades are positioned at an idle pitch angle, the auxiliary power source is charged only when the prevailing wind speed reaches at least a predetermined wind speed. Critical electrical systems may continue to operate for a longer period of time. Alternatively or additionally, the number and / or size of energy storage systems may be reduced.

[0073] In some examples, instead of being in "normal operation," the wind turbine may already be in an autonomous operation mode when decision step 110 is performed. In these examples, determining whether the predetermined condition for idling operation is met may include determining whether the energy level of one or more of the auxiliary power sources is below an energy threshold. If this condition is met, the wind turbine blades 22 may be pitched to a predetermined pitch angle to charge the power storage device. A higher or lower energy threshold may be selected depending on, for example, the wind turbine's location, expected wind speed, expected time without a power grid connection, etc. Once at the idle pitch angle, the pitch angle is kept substantially constant. In other words, no active or passive pitch control is performed. Other suitable conditions may be identified in other examples.

[0074] In some examples, the idle pitch angle may be maintained at least until a condition for ceasing idling operation is detected. For example, when the prevailing wind speed no longer poses a danger to the wind turbine, the wind turbine blades 22 may be pitched away from the idle pitch angle. In some examples, the idle pitch angle may be maintained at least until the wind turbine 10 is able to extract power from the grid, e.g., at least until the wind turbine regains connection with the grid. For example, if the wind turbine is operating in autonomous mode, the wind turbine may be able to regain connection with the grid whenever a grid fault is resolved or grid conditions change. A determination may then be made to maintain or change the blade pitch angle. If the auxiliary power source becomes depleted while the wind turbine is operating in autonomous mode, the autonomous mode can be resumed once sufficient energy is returned to the auxiliary power source. That is, the method may further include restarting the autonomous mode after the auxiliary power source becomes depleted and then charging it above a predetermined wind speed. The idle pitch angle may be maintained as long as necessary. The autonomous mode may be restarted multiple times before the wind turbine is able to at least draw energy from the power grid.

[0075] In some examples, the idle pitch angle may be maintained at least until a stored energy threshold of one or more power sources 84 is reached. For example, the idle pitch angle may be maintained until some or all of the power sources reach an energy storage level of 80%, 90%, 95%, or more. In some of these examples, once the stored energy threshold is reached, e.g., when the power sources are substantially fully recharged, the blades 22 may be pitched to a feather position, e.g., approximately 90°.

[0076] In some examples, the idle pitch angle may be maintained until a predetermined period of time has elapsed. For example, the pitch angle of the blades may be maintained at the idle pitch angle for a first predetermined period of time, and the blades may be changed to a feathered position and maintained in that position for a second predetermined period of time. The first period and the second period of time may occur during idle operation. The second period of time may begin immediately after the first period of time has ended. The first period of time and the second period of time may also alternate. For example, the blades may be maintained at a predetermined idle pitch angle for a first period of time, then the blades may be feathered and maintained for a second period of time, and then the blades may be repositioned and maintained at the idle pitch angle for the first period of time.

[0077] In some examples, the method may further include triggering an alarm if an unsafe condition is detected while the blades are positioned at the idle pitch angle. The alarm may be communicated in any suitable form. For example, the alarm may be an output message, which may be transmitted to a wind turbine operator or a remote operations center. The output message may indicate an unsafe condition, such as excessive wind speed or load. In response to the alarm, the pitch angle 25 of the blades 22 may, in some examples, be (slightly) modified to reduce the risk of damage to the wind turbine. This may not be accommodated as active pitch control, but rather as a slight adaptation of fixed pitch control when excessive wind, load, or other conditions pose a risk to the wind turbine.

[0078] 5 shows a schematic example in which a wind turbine 10 of a wind farm, for example an offshore wind turbine, is connected to a wind farm busbar 101, which is further connected to a power grid 102 by a first switch 103. All wind turbines (not shown) of the wind farm are connected to the wind farm busbar 101. The connection between the power grid 102 and the wind farm busbar 101 is regulated by the first switch 103.

[0079] The wind turbine's generator 42 generates alternating current (AC) power, the frequency of which varies with changing wind conditions. A power converter 104 may be provided to condition the power output from the generator 42 to be suitable for the power grid 102, for example, AC power having a fixed frequency. The power converter 104 may comprise a machine-side converter, a line-side converter, and a DC (direct current) link (not shown) connecting the machine-side converter and the line-side converter.

[0080] The wind turbine generator 42 may, in some examples, be a permanent magnet generator consisting of a generator rotor carrying multiple permanent magnets and a stator. The permanent magnet generator may be directly driven by the wind turbine rotor 18. The generator stator may be connected to a machine-side converter, which may be configured to convert a received AC voltage to a DC voltage that is then supplied to a DC-link. The line-side converter may be configured to convert the DC voltage from the DC-link to a fixed-frequency AC voltage.

[0081] The line-side converter may be connected to the wind farm busbar 101 via a main transformer 105. The main transformer 105 may be configured to step up the voltage provided by the power converter 104, for example to 3.3 kV. The main transformer 105 may, in some examples, be located within the nacelle 16 or tower 15 of the wind turbine. The main transformer 105 may, in other examples, be located in other suitable locations.

[0082] The wind turbine may also include an auxiliary transformer 107 configured to provide a low voltage power source, for example, approximately 400V, to some electrical elements of the wind turbine. The auxiliary transformer 107 may provide power to critical electrical components 108 of the wind turbine, such as, for example, the ventilation system and the temperature control system. The auxiliary transformer 107 may be housed within the nacelle 16 of the wind turbine and may be connected to the main transformer 105.

[0083] A wind farm may be comprised of a substation including, for example, a wind farm transformer that converts power from a wind farm voltage to a grid voltage of a power grid. In some examples, an auxiliary transformer 107 may also be located at the substation. The auxiliary transformer 107 may accordingly provide auxiliary power to multiple wind turbines. The auxiliary transformer 107 may generally be located at any suitable location within the wind farm.

[0084] The one or more auxiliary power sources 84 may be connected to the wind farm busbar 101 via the second switch 106, as in the example of FIG. 5 . The one or more auxiliary power sources 84 may, in some examples, be provided in a wind farm substation. Thus, auxiliary power may be supplied to multiple wind turbines simultaneously. In other examples, the one or more auxiliary power sources 84 may be installed near or inside individual wind turbines to supply power to each wind turbine individually. Not only one or more auxiliary power sources for supplying auxiliary power to a single wind turbine may be provided, but also one or more auxiliary power sources for supplying auxiliary power to two or more wind turbines. In general, any suitable number and location of auxiliary power sources 84 may be selected.

[0085] 5 , the main transformer 105 is configured to receive power from the power grid 102 at a first voltage and to receive power from one or more auxiliary power sources 84 at a second voltage different from the first voltage, e.g., lower than the first voltage. The power grid 102 is configured to supply power to the wind farm busbars 101 during normal operation, and the auxiliary power sources(s) 84 are configured to supply power to the busbars 101, e.g., in the event of a power grid loss. The wind turbine is configured to supply power to the power grid 102 at the first voltage and optionally to supply power to the auxiliary power sources 84 at the second voltage during normal operation of the wind turbine. The wind turbine is configured to supply power to the auxiliary power sources 84 at the second voltage in an autonomous operation mode of the wind turbine.

[0086] If the wind turbine can no longer receive power from the power grid 102, the wind turbine may begin drawing power from one or more auxiliary power sources 84. Critical electrical components 108 of the wind turbine 10 may therefore be supplied with power via the wind turbine's auxiliary transformer 107. The auxiliary wind turbine transformer 107 may transform the power received from the wind turbine's main transformer 105 to the voltage level required by the wind turbine's electrical components it powers, for example from 3.3 kV to 0.4 kV. Thus, the batteries of the power source 84 can be charged when the wind turbine's rotor 18 is rotating above a predetermined wind speed and the blades 22 are at an idle pitch angle.

[0087] The above description can be adapted to the number and location of main transformers 105, auxiliary transformers 107, auxiliary power supplies 84, voltage levels, number of wind turbines 10 drawing / sending power, etc.

[0088] In some examples, an uninterruptible power supply (not shown) may be located with some of the critical electrical components 108. In the event of a loss of the power grid, it may take some time for some of the auxiliary power sources 84 to provide power to the critical electrical components. For example, a diesel generator may need to start and warm up before it can provide full power. The uninterruptible power supply (not shown) may be capable of providing power for, for example, up to about 30 minutes or more. However, by that time, power supply from available auxiliary power sources 84 must be established.

[0089] In a further aspect of the present disclosure, a method 200 for operating a wind turbine 10 is provided. The wind turbine 10 comprises a rotor 18 including a plurality of blades 22 and a generator 42. The wind turbine 10 is configured to deliver electrical power from the generator 42 to one or more auxiliary power sources 84, at least in an autonomous operating mode of the wind turbine. Method 200 is illustrated in the flowchart of Figure 6. Aspects and discussions relating to method 100 may be applied in combination to method 200, and vice versa.

[0090] The method comprises, at block 210, pitching blades 22 to an idle pitch angle when wind turbine 10 is in an autonomous operating mode. The method further comprises, at block 220, idling the wind turbine rotor at a fixed pitch angle corresponding to the idle pitch angle. That is, pitch angle 25 of blades 22 is maintained at the idle pitch angle. The method further comprises, at block 230, charging the auxiliary power source when the rotor rotational speed during idling is equal to or greater than the rotational speed threshold, i.e., when the prevailing wind speed is high enough such that the rotor idles at a high enough speed for power to be generated in the generator (and converted in the power converter) and provided to the auxiliary power source and / or auxiliary components.

[0091] The method further includes, at block 240, changing the pitch angle of the blades when a predetermined (operating) condition is met.

[0092] In some examples, a predetermined condition for idling may be detected before the pitching 210 step is performed. For example, it may be determined whether one or more energy levels of auxiliary power source 84 are at or below an energy threshold. In other examples, pitching 210 may be performed in response to a detected loss of the ability to draw power from the grid. In yet another example, pitching 210 may be performed a predetermined period of time, such as several minutes, after detecting the inability to obtain power from the grid.

[0093] In some examples, the wind turbine 10 may be idled with the blades 22 in a feathered position, e.g., at a pitch angle of about 90°, before the blades 22 are pitched to a predetermined pitch angle, e.g., about 70°, that allows charging of the auxiliary power source.

[0094] The predetermined operating conditions may include one or more of restoring the ability to draw power from the power grid, e.g., restoring connection to the power grid, and triggering an alarm, e.g., due to high wind speed. In some examples, the predetermined pitch angle is a pitch angle such that the wind speed is at least 8 m / s, particularly at least 10 m / s, and more particularly at least 12 m / s.

[0095] In some examples, the predetermined pitch angle is between 55° and 80°.

[0096] In a further aspect of the present disclosure, a wind turbine 10 is provided that is configured to perform any of the methods 100, 200 disclosed herein. The wind turbine 10 includes a rotor 18 that includes a plurality of blades 22, a generator 42, and optionally one or more auxiliary power sources 84. The wind turbine is configured to provide power from the generator 42 to the one or more auxiliary power sources 84, at least in an autonomous operating mode of the wind turbine. In this manner, the auxiliary power sources may be charged when a certain idle condition is detected and the blades 22 are positioned and held at a predetermined pitch position. Note that the wind turbine 10 may be an onshore or offshore wind power generation system.

[0097] The wind turbine 10 may include a control system configured to perform any of the methods described herein.

[0098] This written description discloses the teachings, including preferred embodiments, and uses examples to enable any person skilled in the art to practice the teachings, including making and using any devices or systems and performing any incorporated methods. The patentable scope 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 have structural elements that do not differ from the literal language of the claims, or if they contain equivalent structural elements that do not differ substantially from the literal language of the claims. Aspects from the various described embodiments, and other known equivalents to each such aspect, can be mixed and matched by those skilled in the art to construct additional embodiments and techniques consistent with the principles of the present application. In the claims, where reference signs relating to the drawings are placed within parentheses, they are merely intended to enhance the clarity of the claims and should not be construed as limiting the scope of the claims. [Explanation of symbols]

[0099] 10: Wind turbine 12: Ground 14: Support system 15: Tower 16: Nacelle 18: Rotor 20: Hub 22: Rotor blade 24: Blade root 25: Pitch angle 26: Reference line 26: Load transfer area 27: Chord 28: Wind direction 30: Rotor axis 32: Pitch system 34: Pitch axis 36: Wind turbine control device 38: Yaw axis 42: Generator 43: Communication module 44: Main shaft 45: Rotor speed reference curve 46: Gearbox 48: High speed shaft 50: Coupling 51: Shaft sensor 52: Main frame 53: Generator sensor 54: Decoupling support means 56: Yaw drive mechanism 58: Meteorological measurement system 60: Main forward support bearing 62: Aft support bearing 64: Drive train 66: Pitch assembly 68: Pitch drive system 70: Sensor 72: Pitch bearing 74: Pitch drive motor 76: Pitch drive gearbox 78: Pitch drive pinion 80: Pitch control system 84: Generator 86: Cavity 88: Inner surface 90: Transformer 101: Busbar 102: Power grid 103: Torque arm 104: Power converter 105: Main transformer 107: Auxiliary transformer 108: Electrical component

Claims

1. A method (100) for operating a wind turbine (10) including a wind turbine rotor (18) having a plurality of blades (22) and a wind turbine generator (42), wherein the wind turbine (10) is configured to supply power from the generator (42) to one or more auxiliary power sources (84) in an autonomous operating mode, the method comprising: determining (110) whether predetermined conditions for idling operation of the wind turbine (10) are met; If a predetermined condition for idling operation is satisfied, pitching (120) the blades (22) to an idling pitch angle so that the wind turbine (42) generates power to charge the auxiliary power source (84) while idling at or above a predetermined wind speed; maintaining a pitch angle (25) of the blades (22) at an idle pitch angle during idling; charging an auxiliary power supply (84) when the prevailing wind speed is equal to or greater than a predetermined wind speed; Including, The method includes setting an idle pitch angle in the range of 55 to 75 degrees, and with the blades at this angle, the wind turbine rotor rotates at least 2 RPM at idle when the wind speed is at a predetermined wind speed.

2. 2. The method of claim 1, wherein the idle pitch angle is between 60° and 75°.

3. The method of claim 1 , wherein determining whether conditions for idling are met comprises determining whether an unsafe condition exists.

4. 2. The method of claim 1, wherein determining whether conditions for idling are met includes determining whether conditions for reducing or stopping the supply of power to the power grid are met.

5. The method of claim 4, further comprising reducing or eliminating the supply of power to the power grid (102).

6. The method of claim 1 , wherein determining whether a condition for idling operation is met comprises determining whether the wind turbine (10) is unable to draw power from the power grid (102).

7. The method of claim 1, wherein determining whether the conditions for idling operation are met occurs during normal operation of the wind turbine (10).

8. The method of claim 7 further comprising initiating an autonomous driving mode.

9. The method of claim 1, wherein determining whether the conditions for idling operation are met is performed when the wind turbine (10) is in an autonomous operation mode.

10. 10. The method of claim 9, further comprising resuming the autonomous mode after depletion of the auxiliary power source (84) and thereafter charging above a predetermined wind speed.

11. 10. The method of claim 1, wherein the idle pitch angle is maintained at least until an idle shutdown condition is detected.

12. The method of claim 11, wherein the idling pitch angle is maintained at least until the wind turbine (10) regains connection with the power grid (102).

13. a wind turbine rotor (18) comprising a plurality of blades (22); a generator (42); a control system (36); Including, A wind turbine (10) wherein the control system (36) is configured to carry out a method according to any one of claims 1 to 12.

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