Patent Description:
Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

In case of high wind speeds exceeding the cut-out speed of a wind turbine, in particular under storm conditions, the wind turbine's rotor is usually ideling with the rotor blades positioned at fixed angular positions with respect to their respective pitch axis (pitch position), in particular in the respective so-called feather position (<NUM>° or close to <NUM>°) to limit wind loads that otherwise could exceed a safety margin. For example, the rotor blades of an exemplary rotor with three rotor blades may be at the same pitch position, for example at <NUM>°, or in a so-called staggered position, in which the first blade is at <NUM>°, the second blade is <NUM>° and third rotor blade is at <NUM>°. Due to the ideling mode, the rotor blades can be at any angular position with respect to the rotor axis of the rotor (azimuth position). Document <CIT> describes a method that reduces vibrations of a wind turbine in a situation where yawing of a wind rotor of said wind turbine is at least temporarily not possible. The method includes adjusting a first pitch angle of a first rotor blade and a second pitch angle of a second rotor blade such that the first and second pitch angles differ by at least <NUM> degrees. Further, document <CIT> describes a horizontal axis wind turbine capable of reducing flutter, and by extension, reducing the load on the wind turbine, without controlling the yaw, regardless of the direction of the wind relative to the nacelle. When the wind speed is above a specific value, the yaw angle of the nacelle is held constant, the blade pitch angle is controlled according to the yaw angle of the wind direction relative to the nacelle, and the rotor is allowed to rotate freely. Even when the yaw angle of the nacelle is held constant, allowing the rotor to rotate freely makes it possible to reduce the load by avoiding flutter.

Nevertheless, loads may vary and become comparatively high during idling, respectively, in particular during a prolonged storm. This can create a challenge and imposes high demands on the load capacity of the wind turbine to be considered in the design phase of the wind turbine.

Accordingly, the present disclosure provides a method for operating a wind turbine according to claim <NUM>, a method for designing a wind turbine according to claim <NUM>, and a wind turbine according to claim <NUM>.

The invention is defined by the appended independent claims as follows: a method for operating a wind turbine according to claim <NUM>, and a wind turbine according to claim <NUM>. Further aspects of the invention are defined by the appended dependent claims.

In one aspect, the present disclosure is directed to a method for operating a wind turbine. The wind turbine includes a rotor having rotor blades, and a drive train including a generator and a rotor shaft mechanically connected with the generator and having an axis of rotation. The rotor is mechanically connected with the rotor shaft and rotatable about the axis of rotation. The method includes determining that the generator is not operating in a power generating mode, and operating the rotor to move around a predefined desired angular orientation with respect to the axis of rotation in an alternating fashion.

Accordingly, idling of the rotor and the disadvantages accompanied therewith such as high mechanical loads can be avoided, in particular in high wind conditions, i.e. when the wind speed is higher than allowing for converting wind energy into electrical power using the generator.

Instead the rotor may be controlled to move around a predefined desired angular orientation in which the loads are expected to act on wind turbine components are lower than a maximum value as function of the angular orientation, more typically at least close to a minimum value, when the generator is not in the power generating mode. The terms "power generating mode" and "non-power generating mode" of a generator as used within this specification intend to describe that the generator is used for converting mechanical energy (of then rotor) to electrical energy (power generating mode) and not used for converting mechanical energy (of then rotor) to electrical energy (non-power generating mode), respectively.

Accordingly, mechanical loads acting on the wind turbine components may be reduced at high wind speed in the non-power generating mode. Thus, life time, and/or maintenance intervals may be extended. As a consequence, even the (annual/total) power yield of the wind turbine may be increased without increasing costs.

Further, it may even be possible to operate the generator at higher wind speed in power generating mode (increased cut-out wind speed).

Alternatively or in addition, the corresponding reduced expected loads may be taken into account during a design phase of wind turbines.

Accordingly, one or several components of the wind turbine or even the complete wind turbine can be designed to be lighter and/or more cost-effective.

The loads can be expressed in terms of forces and/or moments acting on various locations in the turbine, in particular on structural or supporting components of the wind turbine, such as the nacelle and the tower, which are in the following also referred to as supporting structure.

The predefined desired angular orientation may be chosen with respect to a predefined measure for the mechanical loads.

The predefined measure typically depends on the particular type and/or design of a wind turbine and may correspond to a weighted measure, e.g. a weighted sum of the forces and/or moments acting at one or more locations of the wind turbine, in particular locations at the drive train and at supporting structure(s) including bearings of the wind turbine such as the tower and the nacelle.

Further, the forces and/or moments may be determined for varying wind speeds and/or varying wind directions and/or may represent respective maximum or averaged values.

Typically, the rotor is operated in a predefined angle range including the predefined desired angular orientation.

Accordingly, lubricating of components, in particular bearings is facilitated. Consequently, damaging resulting from insufficient lubricating and/or longer still stand such as false brinelling can be avoided.

The predefined angle range may be symmetric with respect to the predefined desired angular orientation and/or may, for a rotor with three rotor blades, be a most <NUM>°, more typically at most <NUM>°, and even more typically a least <NUM> ° or even <NUM>° wide.

Operating the rotor to move around the predefined desired angular orientation and within the predefined angle range, respectively, in an alternating fashion typically includes reversing a direction of movement at least once, more typically at least two or at least three times.

Moving the rotor around the predefined desired angular orientation and within the predefined angle range, respectively, is may be but is typically not a periodic movement, e.g. due to the fluctuating wind.

For example, operating the rotor in the alternating fashion may include operating the rotor to move around the predefined desired angular orientation and within the predefined angle range, respectively, in an oscillating fashion, typically in a non-periodic oscillating fashion.

Determining that the generator is not operating in a power generating mode may include stopping an electric power generation of the generator and/or determining that the rotor is idling.

The electric power generation of the generator may be stopped after determining a fault condition, in particular a fault condition limiting or even preventing power conversion by the generator. The fault condition may be a fault condition of the wind turbine (internal fault condition), a fault condition referring to a windfarm the wind turbine belongs to, or a fault condition of a grid (grid fault) the wind turbine and the windfarm, respectively, is connected to.

The method for operating the wind turbine typically includes determining that a speed of the wind in front of and/or acting on the rotor is equal to or larger than a predefined threshold value prior to operating the rotor to move around the predefined desired angular orientation and within the predefined angle range, respectively.

This may include measuring the wind speed with an anemometer, a LIDAR or the like of the wind turbine or the windfarm respectively.

Further, an actual angular orientation of the rotor with respect to the axis of rotation may be determined, in particular after determining that the rotor is idling, after determining the fault condition, after stopping the electric power generation and/or when the speed of a wind is equal to or larger than the predefined threshold value.

If the actual angular orientation of the rotor is not close to the predefined desired angular orientation and not within the predefined angle range, respectively, the rotor may be transferred towards the predefined desired angular orientation.

In one embodiment, the threshold value is equal to or larger than a cut-out wind speed of the wind turbine.

In a further embodiment, the threshold value is smaller than the cut-out wind speed of the wind turbine. In this embodiment, the rotor is typically only transferred towards the predefined desired angular orientation and/or moved around the predefined desired angular orientation and within the predefined angle range, respectively, after determining a fault condition as explained above.

Further, the control may be based on two different threshold values for the wind speed, a first one lower than the cut-out wind speed of the wind turbine, and a second one corresponding to the cut-out wind speed or being somewhat higher, e.g. up to <NUM>% <NUM>% or even <NUM>% higher than the cut-out wind speed.

The method for operating the wind turbine may further include determining a duration of operating the rotor to move around the predefined desired angular orientation and within the predefined angle range, respectively.

Further, on or after detecting that the determined duration is equal to or larger than a predefined time interval of e.g. a few seconds, a few ten seconds or even up to several minutes, the rotor may be transferred towards a further predefined desired angular orientation with respect to the axis of rotation.

Thereafter, the rotor may be operated to move around the further predefined desired angular orientation and within a further predefined angle range, respectively, in an alternating fashion.

Accordingly, the loads acting on the wind turbine may be more evenly distributed. Further, this may facilitate lubricating of bearings and the like even further.

Typically, the further predefined desired angular orientation is, due to a symmetry of the rotor, equivalent to the predefined desired angular orientation.

Likewise, the further predefined angle range may correspond to the predefined angle range but shifted.

For example, the further predefined desired angular orientation may deviate from the predefined desired angular orientation by +/- <NUM>° in embodiments referring to operating wind turbines having a three-blade rotor.

In these embodiments, the further predefined angle range may correspond to the predefined angle range shifted by +/- <NUM>°.

Transferring the rotor towards the predefined desired angular orientation, operating the rotor to move around the predefined desired angular and/or within the predefined desired angular orientation, transferring the rotor towards the further predefined desired angular orientation, and/or operating the rotor to move around the further predefined desired angular orientation and/or within the further predefined desired angular orientation may include and/or be achieved by pitching one of the rotor blades.

Typically, not all of the rotor blades are pitched during pitching the rotor blades, at least not simultaneously.

For example, only one of the rotor blades may be pitched a time to achieve the desired rotor movement.

Accordingly, energy consumption during this mode of operation may be reduced. This may be of particular importance, if an internal energy storage, in the following also referred to as (internal) power source, such as a battery of the wind turbine has to be used for energy supply, e.g. due to a grid fault.

Further, the rotor blade pitched at a time may change after a given time interval.

During pitching, a pitch angle range of the rotor blade(s) is typically also limited to a predefined range, for example to the feather position +/- <NUM>° or +/- <NUM>°.

Accordingly, the energy consumption may be further reduced.

Alternatively or in addition, a parking brake of the wind turbine or even the generator may be used to achieve the desired respective movement of the rotor.

For example, the generator rotor may be allowed to accelerate and decelerate within in certain limits to influence the rotor movement.

Further, the parking brake may be used to decelerate the rotor if desired.

In another aspect, the present disclosure is directed to a method for designing a wind turbine including a supporting structure, a drive train supported by the supporting structure, and a rotor having rotor blades. The drive train includes a generator and a rotor shaft mechanically connected with the generator and having an axis of rotation. The rotor is mechanically connected with the rotor shaft and rotatable about the axis of rotation. The method includes determining, for a given configuration of the wind turbine and assuming that the generator is not operating in a power generating mode while a wind acts on the rotor in a direction which is at least on average at least substantially parallel to the axis of rotation, a desired angular orientation so that a predefined measure for mechanical loads acting on the drive train and/or the supporting structure is expected to be lower when the rotor is at the desired angular orientation compared to another angular orientation of the rotor with respect to the axis of rotation, typically at least close to a minimum, more typically at least close to a global minimum.

The term "configuration of a wind turbine" as used herein intends to embrace the terms "model of the wind turbine", "design of the wind turbine" and "layout of the wind turbine". For example, the configuration of the wind turbine may include a model describing the mechanical properties of the wind turbine, in particular of the rotor (including the blades), the drive train, the generator and/or supporting structures, including their respective response under mechanical load.

The method for designing the wind turbine typically includes using the measure for the mechanical loads and/or the mechanical loads to determine desired material properties and/or desired geometric properties of the configuration so that the wind turbine is expected to safely withstand the wind when the rotor is operated at least close to desired angular orientation, e.g. moved around the predefined desired angular orientation in an alternating fashion and within an additionally determined (predefined) angle range, even if a speed of the wind reaches an expected maximum value and/or is fluctuating.

Determining the desired angular orientation of the rotor and/or using the measure for the mechanical loads and/or the mechanical loads may include one or more of the following steps:.

Typically, the methods as explained herein are performed for a wind turbine with a rotor having three rotor blades.

For example, determining the desired angular orientation typically includes calculating the predefined measure for the mechanical loads for a plurality of rotor orientations which are at least close to a Y-position of a rotor with three rotor blades, e.g. calculating the predefined measure for the mechanical loads in an angle range of +/-<NUM>° or even +/-<NUM>° around the Y-position.

In another aspect, the present disclosure is directed to a wind turbine. The wind turbine includes a drive train including a generator and a rotor shaft having an axis of rotation and being mechanically connected with the generator. The wind turbine further includes a rotor including rotor blades, being mechanically connected with the rotor shaft and rotatable about the axis of rotation, at least one device for influencing a rotational movement of the rotor about the axis of rotation, and a controller connected with the generator and the at least one device for influencing the rotational movement of the rotor. The controller is configured to set the generator into a non-power generating mode and to control the at least one device such that the rotor moves around a predefined desired angular orientation with respect to the axis of rotation in an alternating fashion.

The term "device for influencing a rotational movement of the rotor" shall describe a device that is configured to exert and/or change a torque acting on the rotor, in particular a torque in direction of the axis of rotation.

Typically, the controller is configured to control the at least one device such that the rotor moves within a predefined angle range including the predefined desired angular orientation.

The controller may be configured to control the rotor movement around the desired angular orientation when a speed of the wind in front of and/or acting on the rotor is equal to or larger than a predefined threshold value.

For this purpose, the wind turbine may include a first sensor which is connected with the controller for measuring a value correlated with a speed of the wind in front of and/or acting on the rotor.

The wind turbine may further include a second sensor which is connected with the controller for measuring an actual angular orientation of the rotor with respect to the axis of rotation, for example a sensor for measuring an orientation of the rotor shaft.

Accordingly, the controlling the rotational movement of the rotor about the axis of rotation may be facilitated, for example performed as a close-loop control.

Typically, the wind turbine includes a pitch drive system coupled to the rotor blade(s) and controllable by the controller to provide a respective device for influencing the rotational movement of the rotor.

Alternatively or in addition, the wind turbine may include a rotor brake which is controllable by the controller to provide a respective device for influencing the rotational movement of the rotor.

Furthermore, the generator may be controllable by the controller to provide a respective device for influencing the rotational movement of the rotor.

Even further, the wind turbine may include a power source connected with the at least one device for power supply, in particular during an electrical power loss event of the wind turbine.

Alternatively or in addition, the at least one device may be supplied with electric power by a power backup provided by the wind farm.

Typically, the controller is configured to perform any of the processes of the methods for operating a wind turbine as explained herein.

In embodiments referring to wind turbines with a three-bladed rotor, the desired angular orientation may correspond to a Y-position of the rotor, but may also close to, but differ from the Y-position of the rotor, for example by up to several degrees or even up to about <NUM> °.

The wind turbine may be an onshore wind turbine or an offshore wind turbine.

Other embodiments include corresponding computer-readable storage media or storage devices, and computer programs recorded on one or more computer-readable storage media or storage devices, respectively, configured to perform the processes of the methods described herein.

In particular, a computer program product and/or a computer-readable storage medium may include instructions which, when executed by a one or more processors of a system, such as a controller of a wind turbine, cause the system to carry out the processes of the methods explained herein.

The system of and/or including one or more computers and/or processors can be configured to perform particular operations or processes by virtue of software, firmware, hardware, or any combination thereof.

These and other features, aspects and advantages of the present invention will be further supported and described with reference to the following description and appended claims.

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which refers to the appended figures, in which:.

Single features depicted in the figures are shown relatively with regards to each other and therefore are not necessarily to scale. Similar or same elements in the figures, even if displayed in different embodiments, are represented with the same reference numbers.

<FIG> is a perspective view of an exemplary wind turbine <NUM>. In the exemplary embodiment, the wind turbine <NUM> is a horizontal-axis wind turbine. In the exemplary embodiment, the wind turbine <NUM> includes a tower <NUM> that extends from a support system <NUM>, a nacelle <NUM> mounted on tower <NUM>, and a rotor <NUM> that is coupled to nacelle <NUM>. In the exemplary embodiment, the rotor <NUM> has three rotor blades <NUM>. In the exemplary embodiment, the tower <NUM> is fabricated from tubular steel to define a cavity (not shown in <FIG>) between a support system <NUM> and the nacelle <NUM>.

In one embodiment, the rotor blades <NUM> have a length ranging from about <NUM> meters (m) to about <NUM>. Alternatively, rotor blades <NUM> may have any suitable length that enables the wind turbine <NUM> to function as described herein. For example, other non-limiting examples of blade lengths include <NUM> or less, <NUM>, <NUM>, <NUM>, <NUM> or a length that is greater than <NUM>. As wind strikes the rotor blades <NUM> from a wind direction <NUM>, the rotor <NUM> is rotated about an axis of rotation <NUM>. As the rotor blades <NUM> are rotated and subjected to centrifugal forces, the rotor blades <NUM> are also subjected to various forces and moments. As such, the rotor blades <NUM> may deflect and/or rotate from a neutral, or non-deflected, position to a deflected position.

Moreover, a pitch angle of the rotor blades <NUM>, i.e., an angle that determines a perspective of the rotor blades <NUM> with respect to the wind direction, may be changed by a pitch system <NUM> to control the load and power generated by the wind turbine <NUM> by adjusting an angular position of at least one rotor blade <NUM> relative to wind vectors. During operation of the wind turbine <NUM>, the pitch system <NUM> may change a pitch angle of the rotor blades <NUM> such that the rotor blades <NUM> are moved to a feathered position, such that the perspective of at least one rotor blade <NUM> relative to wind vectors provides a minimal surface area of the rotor blade <NUM> to be oriented towards the wind vectors, which facilitates reducing a rotational speed and/or facilitates a stall of the rotor <NUM>.

In the exemplary embodiment, a blade pitch of each rotor blade <NUM> is controlled individually by a wind turbine controller <NUM> or by a pitch control system <NUM>.

Further, in the exemplary embodiment, as the wind direction <NUM> changes, a yaw direction of the nacelle <NUM> may be rotated about a yaw axis <NUM> to position the rotor blades <NUM> with respect to wind direction <NUM>.

In the exemplary embodiment, the wind turbine controller <NUM> is shown as being centralized within the nacelle <NUM>, however, the wind turbine controller <NUM> may be a distributed system throughout the wind turbine <NUM>, on the support system <NUM>, within a wind farm, and/or at a remote control center. The wind turbine controller <NUM> includes a processor <NUM> configured to perform the methods and/or steps described herein. Further, many of the other components described herein include a processor. As used herein, the term "processor" is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and/or a control system can also include memory, input channels, and/or output channels.

<FIG> is an enlarged sectional view of a portion of the wind turbine <NUM>. In the exemplary embodiment, the wind turbine <NUM> includes the nacelle <NUM> and the rotor <NUM> that is rotatably coupled to the nacelle <NUM>. More specifically, the hub <NUM> of the rotor <NUM> is rotatably coupled to an electric generator <NUM> positioned within the nacelle <NUM> by the main shaft <NUM>, a gearbox <NUM>, a high speed shaft <NUM>, and a coupling <NUM>. In the exemplary embodiment, the main shaft <NUM> is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle <NUM>. A rotation of the main shaft <NUM> drives the gearbox <NUM> that subsequently drives the high speed shaft <NUM> by translating the relatively slow rotational movement of the rotor <NUM> and of the main shaft <NUM> into a relatively fast rotational movement of the high speed shaft <NUM>. The latter is connected to the generator <NUM> for generating electrical energy with the help of a coupling <NUM>.

The gearbox <NUM> and generator <NUM> may be supported by a main support structure frame of the nacelle <NUM>, optionally embodied as a main frame <NUM>. The gearbox <NUM> may include a gearbox housing <NUM> that is connected to the main frame <NUM> by one or more torque arms <NUM>. In the exemplary embodiment, the nacelle <NUM> also includes a main forward support bearing <NUM> and a main aft support bearing <NUM>. Furthermore, the generator <NUM> can be mounted to the main frame <NUM> by decoupling support means <NUM>, in particular in order to prevent vibrations of the generator <NUM> to be introduced into the main frame <NUM> and thereby causing a noise emission source.

Preferably, the main frame <NUM> is configured to carry the entire load caused by the weight of the rotor <NUM> and components of the nacelle <NUM> and by the wind and rotational loads, and furthermore, to introduce these loads into the tower <NUM> of the wind turbine <NUM>.

The gearbox <NUM> may be accompanied by a gearbox system which also may comprise a reservoir for lubricant for lubricating gears and rotation bearings of the gearbox <NUM>, lubricant duct arrangements, a lubricant pump a filter device and/or a cooling device for the lubricant.

However, the present disclosure is not limited to a wind turbine comprising a gearbox, but also wind turbines without a gearbox, thus, heading a so-called direct drive may be concerned as well.

For positioning the nacelle appropriately with respect to the wind direction <NUM>, the nacelle <NUM> may also include at least one meteorological mast <NUM> that may include a wind vane and (neither shown in <FIG>). The mast <NUM> provides information to the wind turbine controller <NUM> that may include wind direction and/or wind speed.

In the exemplary embodiment, the pitch system <NUM> is at least partially arranged as a pitch assembly <NUM> in the hub <NUM>. The pitch assembly <NUM> includes one or more pitch drive systems <NUM> and at least one sensor <NUM>. Each pitch drive system <NUM> is coupled to a respective rotor blade <NUM> (shown in <FIG>) for modulating the pitch angle of a rotor blade <NUM> along the pitch axis <NUM>. Only one of three pitch drive systems <NUM> is shown in <FIG>.

In the exemplary embodiment, the pitch assembly <NUM> includes at least one pitch bearing <NUM> coupled to hub <NUM> and to a respective rotor blade <NUM> (shown in <FIG>) for rotating the respective rotor blade <NUM> about the pitch axis <NUM>. The pitch drive system <NUM> includes a pitch drive motor <NUM>, a pitch drive gearbox <NUM>, and a pitch drive pinion <NUM>. The pitch drive motor <NUM> is coupled to the pitch drive gearbox <NUM> such that the pitch drive motor <NUM> imparts mechanical force to the pitch drive gearbox <NUM>. The pitch drive gearbox <NUM> is coupled to the pitch drive pinion <NUM> such that the pitch drive pinion <NUM> is rotated by the pitch drive gearbox <NUM>. The pitch bearing <NUM> is coupled to pitch drive pinion <NUM> such that the rotation of the pitch drive pinion <NUM> causes a rotation of the pitch bearing <NUM>.

Pitch drive system <NUM> is typically coupled to the wind turbine controller <NUM> for adjusting the pitch angle of a rotor blade <NUM> upon receipt of one or more signals from the wind turbine controller <NUM>. In the exemplary embodiment, the pitch drive motor <NUM> is any suitable motor driven by electrical power and/or a hydraulic system that enables pitch assembly <NUM> to function as described herein. Alternatively, the pitch assembly <NUM> 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 <NUM> is driven by energy extracted from a rotational inertia of hub <NUM> and/or a stored energy source (not shown) that supplies energy to components of the wind turbine <NUM>.

The pitch assembly <NUM> also includes one or more pitch control systems <NUM> for controlling the pitch drive system <NUM> according to control signals from the wind turbine controller <NUM>, in case of specific prioritized situations and/or during rotor <NUM> overspeed. In the exemplary embodiment, the pitch assembly <NUM> includes at least one pitch control system <NUM> communicatively coupled to a respective pitch drive system <NUM> for controlling pitch drive system <NUM> independently from the wind turbine controller <NUM>. In the exemplary embodiment, the pitch control system <NUM> is coupled to the pitch drive system <NUM> and to a sensor <NUM>. During normal operation of the wind turbine <NUM>, the wind turbine controller <NUM> controls the pitch drive system <NUM> to adjust a pitch angle of rotor blades <NUM>.

In one embodiment, in particular when the rotor <NUM> operates at rotor overspeed, the pitch control system <NUM> overrides the wind turbine controller <NUM>, such that the wind turbine controller <NUM> no longer controls the pitch control system <NUM> and the pitch drive system <NUM>. Thus, the pitch control system <NUM> may be able to make the pitch drive system <NUM> to move the rotor blade <NUM> to a feathered position for reducing a rotational speed of the rotor <NUM>.

According to an embodiment, an internal power source <NUM>, for example comprising an electrical energy storage, in particular a battery and/or electric capacitors, is arranged at or within the hub <NUM> and is coupled to the sensor <NUM>, the pitch control system <NUM>, to the pitch drive system <NUM> and the yaw drive mechanism <NUM> to provide a source of power to these components. The internal power source <NUM> may also be a distributed power source. In particular, internal power source <NUM> may include an internal power source for the pitch assembly <NUM> and an internal power source for the yaw drive mechanism <NUM>.

In the exemplary embodiment, the power source <NUM> provides a continuing source of power at least to the pitch assembly <NUM> during operation of the wind turbine <NUM>. In an alternative embodiment, power source <NUM> provides power to at least to the pitch assembly <NUM> only during an electrical power loss event of the wind turbine <NUM>. In this embodiment, the electrical power is also referred to as backup power source and emergency power supply, respectively. The electrical power loss event may include power grid loss or dip, malfunctioning of an electrical system of the wind turbine <NUM>, and/or failure of the wind turbine controller <NUM>. During the electrical power loss event, the power source <NUM> operates to provide electrical power to the pitch assembly <NUM> such that pitch assembly <NUM> can operate during the electrical power loss event. However, the power source <NUM> and backup power source <NUM>, respectively, may also provide electrical power the other components, in particular the yaw drive mechanism <NUM>. In this regard it should be noted that the wind turbine controller <NUM> is typically provided with a separate backup power source, for example an uninterruptible power supply (UPS).

In the exemplary embodiment, the pitch drive system <NUM>, the sensor <NUM>, the pitch control system <NUM>, cables, and the power source <NUM> are each positioned in a cavity <NUM> defined by an inner surface <NUM> of hub <NUM>. In an alternative embodiment, said components are positioned with respect to an outer surface <NUM> of hub <NUM> and may be coupled, directly or indirectly, to outer surface <NUM>.

Furthermore, power source <NUM> may be electrically connected with or even be provided by an external power supply different to the grid, in particular by an emergency power network of the wind farm the wind turbine <NUM> belongs to, and/or a wind farm power source typically comprising a diesel aggregate, battery(ies) and/or electric capacitor(s).

<FIG> are front views of wind turbine <NUM> corresponding to two different angular orientation α of rotor <NUM> with respect to the rotational axis <NUM> shown in <FIG>. In the following the rotational axis <NUM> is also referred to as rotor axis.

In the exemplary embodiment, the angular orientation α of rotor <NUM> is measured with respect to a Y-position of rotor <NUM> shown in <FIG>, in which a first rotor blade 22a of the three exemplary rotor blades 22a, 22b, 22c is with its blade tip at the lowest possible point and substantially vertically orientated. In this embodiment, the angular orientation α of rotor <NUM> is measured in terms of the angular orientation αa of first rotor blade 22a.

However, which of the rotor blades 22a, 22b, 22c is used as reference is not important.

Further, the angular orientation α of rotor <NUM> may also be determined differently, for example as angle between yaw axis <NUM> and a pitch axis of one of the rotor blades, such as pitch axis 34a of first rotor blade 22a, in projection onto the rotor plane defined by rotor axis <NUM>.

Other definitions of the reference angular orientation (α=<NUM>°) are also possible, for example a reference orientation of the rotor axis may be used for this purpose.

As illustrated in <FIG>, rotor <NUM> may be operated close to a predefined desired angular orientation αdes with respect to the rotor axis <NUM> when the generator of the wind turbine is not used for converting wind power into electrical power.

This is typically achieved by pitching one or more rotor blades 22a-22c, in the embodiment illustrated in <FIG> by pitching first rotor blade 22a round its pitch axis 34a.

For this purpose, the corresponding pitch angle βa may be limited two predefined pitch angle range.

The predefined desired angular orientation αdes is typically chosen such that mechanical loads expected to act on wind turbine components, in particular supporting components of wind turbine <NUM> are at least on average close to a minimum value, more typically lowest, when the wind-exposed rotor <NUM> is at the predefined desired angular orientation while the generator is not in a power operating mode.

Typically, rotor <NUM> is moved around the predefined desired angular orientation αdes, more typically in an alternating and/or oscillating manner.

Even more typically, the movement of rotor <NUM> is limited to a predefined angle range around the predefined desired angular orientation αdes in this mode.

As further illustrated in <FIG> and in more detail in <FIG>, the predefined desired angular orientation αdes may be close but different to the Y-position α=<NUM>° of wind turbine <NUM>.

<FIG> illustrates mechanical loads M, F in arbitrary units acting on supporting components of an exemplary wind turbine was three rotor blades as shown in <FIG> as function of the angular rotor orientation α around the Y-position α=<NUM>°.

Dots corresponds to respective weighted sums of values for the mechanical loads M, F (torques M and forces F) acting on different component under a given wind condition that where obtained using a numerical simulation of a model describing the mechanical properties of the wind turbine. The shown curve corresponds to a least square fit of the dots.

In the exemplary embodiment, the load-curve (M, F as function of α) has, in the relevant range of <NUM>°, several maxima and minima, in particular the global minimum at αmin1 of about <NUM>° and is a local minimum at αmin2 of about <NUM>°.

In the exemplary embodiment, lowest mechanical loads are to be expected at rotor position of αmin1+n* <NUM>° with n being whole number. Accordingly, αmin1 it is typically chosen as predefined desired angular orientation αdes.

Further, the shown numerically obtained results are typically used to determine a predefined angle range Δα in which the rotor is to be operated when the generator is not operating in a power generating mode and/or a wind speed in front of and/or acting on the rotor is equal to or larger than a predefined threshold value, in particular a cut-out wind speed of the wind turbine plus some optional margin of e.g. <NUM>% to <NUM>%, more typically <NUM>% to <NUM>%.

However, these values typically depend on the particular design of the wind turbine.

This applies in particular to the determined desired angular orientation αdes as well as the determined predefined angle range Δα.

Note that the asymmetry of the shown numerically obtained results with respect to the is mainly due to the particular airfoils of the three (identical) rotor blades.

As can further be seen from the numerically obtained results in <FIG>, the loads M, F can be significantly reduced, when the rotor is operated to move around the determined predefined desired angular orientation αdes in an alternating fashion while the generator is not in a power operating mode, and/or when the rotational rotor movements are limited to the determined predefined angle range Δα while the generator is not in a power operating mode.

For example, the loads M, F may be reduced in this mode by up to <NUM>% or even up to <NUM>% compared to operating the rotor in an idling mode (without controlling the rotor orientation).

This is of particular importance for high wind conditions (storm conditions), and also typically depends on the particular design of the wind turbine.

Further, the achievable load savings may also depend on the location of the wind turbine, in particular the (expected) wind profile at the location typically also taken into account for determining the desired angular orientation αdes and/or the desired angle range Δα.

<FIG> shows a typical rotor orientation α of a rotor of a wind turbine as shown in <FIG> as function of time t while the generator is not in a power operating mode. The illustrated time interval typically corresponds to about a quarter of an hour.

In the illustrated time interval, the rotor is initially moved within the desired angle range Δα around a second one of three equivalent desired angular orientations αdes + (k-<NUM>)*<NUM>° of the rotor in an (non-periodic) alternating/oscillatory manner, wherein the second rotor blade (k=<NUM>) is the lowest one of the three rotor blades.

The three equivalent desired angular orientations αdes + (k-<NUM>)* <NUM>° of the rotor may be determined as explained above with regard to <FIG>.

When a duration of operating the rotor <NUM> to move within the desired angle range Δα around the second desired angular orientations αdes + <NUM>° reaches a predefined time interval Δt<NUM> of e.g. at least one minute, more typically at least <NUM> up to <NUM>, <NUM> or even <NUM>, the rotor is transferred into the desired angle range Δα around a third one of the three equivalent desired angular orientations αdes + (<NUM>-<NUM>)*<NUM>° and afterwards operated therein in an oscillatory manner, wherein the third rotor blade (k=<NUM>) is the lowest one of the three rotor blades.

When a duration of operating the rotor <NUM> to move within the desired angle range Δα around the third desired angular orientations αdes + <NUM>° reaches the predefined time interval Δt<NUM>, the rotor is transferred into the desired angle range Δα around a first one of the three equivalent desired angular orientations αdes and afterwards operated therein in an oscillatory manner, wherein the first rotor blade (<NUM>=<NUM>) is the lowest one of the three rotor blades.

This may be repeated (also with varying order of rotor blades in lowest position) until e.g. the generator is switchable/switched into the power generating mode.

<FIG> is a flow diagram of a method <NUM> of operating a wind turbine as explained above with regard to <FIG>.

In a first block <NUM>, it is determined, typically by a controller of the wind turbine, that the generator of the wind turbine is not operating in a power generating mode. This may include explicitly setting the generator in a non-power generating mode.

Thereafter, the rotor is operated to move around a predefined desired angular orientation with respect to the rotor axis, typically in an alternating fashion, e.g. similar as explained above with regard to <FIG>.

<FIG> is a flow diagram of a method <NUM> of operating a wind turbine as explained above with regard to <FIG>. Method <NUM> is similar to method <NUM> explained above with regard to <FIG>. However, prior to operating the rotor to move around the predefined desired angular orientation in block <NUM>, it is determined that the rotor is idling (and thus the generator not used for power conversion) in a block <NUM> of method <NUM>.

<FIG> is a flow diagram of a method <NUM> of operating a wind turbine as explained above with regard to <FIG>. Method <NUM> is similar to methods <NUM>, <NUM> explained above with regard to <FIG>.

However, it is first checked if certain condition(s) are met in a decision block <NUM>, <NUM> for actually stopping an electric power generation of the generator in a block <NUM> and subsequently operating the rotor to move around the predefined desired angular orientation(s) in block <NUM>.

In decision block <NUM>, <NUM> it may be checked if the wind speed in front of the rotor is equal to or larger than one or more threshold values vthreshold.

For example, if the wind speed is higher than a cut-out wind speed of the wind turbine, block <NUM>, <NUM> typically determines that the condition(s) is met ("yes").

Further, if a fault is detected challenging or forbidding power conversion of the generator and/or the wind speed is high enough (but lower than the cut-out wind speed), block <NUM>, <NUM> may also determine that the condition(s) is met ("yes").

In other cases, block <NUM>, <NUM> may determine that the condition(s) is not met ("no").

<FIG> is a flow diagram of a method <NUM> of operating a wind turbine as explained above with regard to <FIG>. Method <NUM> is similar to method <NUM> explained above with regard to <FIG>.

However, prior to operating the rotor to move around the predefined desired angular orientation(s) in block <NUM>, the rotor is transferred towards and/or into the predefined desired angular orientation in a block <NUM>, in particular after determining that the rotor is idling, after detecting a fault condition, after stopping the electric power generation and/or when the speed of a wind is equal to or larger than a predefined threshold value Vthreshold.

However, prior to transferring the rotor towards the predefined desired angular orientation in block <NUM>, it is determined that an actual angular orientation of the rotor is not at least close the predefined desired angular orientation, in particular outside a predefined angle range around the predefined desired angular orientation.

Further, it is typically checked if a duration of operating the rotor to move around the predefined desired angular orientation in block <NUM> is equal to or larger than a predefined time interval Δt<NUM>. If so, the rotor is transferred towards a further (equivalent) predefined desired angular orientation with respect to the rotor axis in a block <NUM>.

Subsequently, the rotor may be operated to move around the further predefined desired angular orientation.

<FIG> illustrates a flow diagram of a method <NUM> for designing a wind turbine as explained above with regard to <FIG>.

In a block <NUM>, for a given configuration of the wind turbine and assuming that the generator of the wind turbine is not in a power generating mode while a wind acts on the rotor, a desired angular orientation of the rotor with respect to its axis of rotation is determined so that a predefined measure for mechanical loads acting on a drive train and/or a supporting structure for the rotor and the drive train is expected to be lower when the rotor is at the desired angular orientation compared to other angular orientation(s) of the rotor with respect to its axis of rotation, in particular at least close to a minimum value.

In a subsequent block <NUM>, the determined measure for the mechanical loads and/ or the mechanical loads are used to calculate desired material properties and/or desired geometric properties of the configuration so that the wind turbine is expected to safely withstand the wind when the rotor is operated at least close to desired angular orientation, in particular within an angle range around a desired angular orientation that may also be determined in block <NUM>, even if a speed of the wind reaches an expected maximum value and/or is fluctuating.

As indicated by the dashed arrow in <FIG>, the blocks <NUM> and <NUM> may be repeated, for example several times.

Prior to a new cycle (entering block <NUM>), the configuration of the wind turbine is typically updated in accordance with the calculated material properties and/or desired geometric properties.

Typically, the blocks <NUM> and <NUM> are repeated until one or more convergence criteria are met and/or the number of cycles reaches a threshold value.

The respective convergence criteria may e.g. refer to the measure for the mechanical loads and/or the desired angular orientation.

<FIG> illustrates a schematic view of a wind turbine <NUM> which is typically similar to wind turbine <NUM> explained above with regard to <FIG> and may even represent wind turbine <NUM>.

Wind turbine <NUM> includes a rotor <NUM> including a rotor axis <NUM> and rotor blades, a drive train <NUM> including a generator <NUM> mechanically connected with rotor <NUM>, one or more device D for influencing a rotational movement of the rotor about the rotor axis, and a controller <NUM> connected with the generator <NUM> and the device D. The controller <NUM> is configured to set the generator <NUM> into a non-power generating mode, and to control the one or more devices D such that the rotor <NUM> moves around a desired angular orientation with respect to the rotor axis <NUM>, in particular in an alternating and/ or oscillating fashion.

As indicated by the dashed arrows in <FIG>, wind turbine <NUM> may have a first sensor S1 for measuring a value correlated with a speed of the wind <NUM> in front of rotor <NUM>, and/or a second sensor S2 for measuring an actual angular orientation α of rotor <NUM>, which are connected with the controller for transfer of data (measurement values).

Further, the controller <NUM> may be configured to use measured values received from the first sensor S1 to determine that the speed of wind <NUM> is equal to or larger than a threshold value, and depending thereon to control, using measured values received from the second sensor S2, the one or more devices D such that the rotor <NUM> moves around the desired angular orientation.

Typically, controller <NUM> only uses one, several or even all pitch drive systems each coupled to a respective rotor blades as a respective device D for influencing the rotational movement of the rotor via pitching the rotor blade(s), more typically only one pitch drive system at a time.

However, a rotor brake of wind turbine <NUM> and/or even generator <NUM> may alternatively or more typically additionally be used for this purpose.

Further, the controller <NUM> is typically configured to perform any of the processes of the operating/controlling methods as explained herein.

According to an embodiment of a method for operating a wind turbine comprising a generator at high wind speed, in particular in a storm conditions, and/or for designing the wind turbine to be safely operable at the high wind speed, the method includes determining, assuming that the generator is not operating in a power generating mode, a desired angular orientation of the rotor with respect to its axis of rotation so that a mechanical load acting on the rotor and/or other components of the wind turbine, in particular a supporting structure for the generator and/or the rotor such as a nacelle and a tower of the wind turbine, is expected to be lower than in other angular orientation of the rotor with respect to the axis of rotation.

According to an embodiment of a method for operating a wind turbine including a rotor shaft having an axis of rotation, a generator rotor mechanically connected with the rotor shaft, and a rotor mechanically connected with the rotor shaft, rotatable about the axis of rotation, and having rotor blades, the method includes determining that a speed of a wind in front of and/or acting on the rotor is equal to or larger than a predefined threshold value which is typically equal to or larger than a cut-out wind speed of the wind turbine; and operating the rotor at least close to a predefined desired angular orientation with respect to the axis of rotation while the generator is not operating in a power generating mode. At the desired angular orientation, a mechanical load acting on the rotor and/or other components of the wind turbine, in particular a supporting structure for the generator, the rotor and/or the rotor shaft such as a nacelle and a tower, is expected to be lower than in another angular orientation of the rotor with respect to the axis of rotation, typically at least close to a minimum value, when the generator is not operating in a power generating mode.

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. For example, while the written description refers to horizontal axis wind turbines, the embodiments may also refer to vertical axis wind turbines, in particular variable pitch vertical axis wind turbines. Accordingly, operating the rotor to move around a predefined desired angular orientation with respect to the axis of rotation of the rotor in an alternating fashion while the generator is not in a power operating mode may both applied to horizontal axis wind turbines and vertical axis wind turbines. Such other examples are intended to be within the scope of the claims if they include elements that do not differ from the literal language of the claims.

Claim 1:
A method (<NUM>-<NUM>) for operating a wind turbine (<NUM>, <NUM>) comprising a drive train (<NUM>) comprising a generator (<NUM>) and a rotor shaft (<NUM>) mechanically connected with the generator (<NUM>) and comprising an axis (<NUM>) of rotation, and a rotor (<NUM>) comprising rotor blades (<NUM>-22c), the rotor (<NUM>) being mechanically connected with the rotor shaft (<NUM>) and rotatable about the axis (<NUM>) of rotation, the method (<NUM>-<NUM>) comprising:
- determining (<NUM>) that the generator (<NUM>) is not operating in a power generating mode;
the method being characterized in that it further comprises:
- operating (<NUM>) the rotor (<NUM>) to move around a predefined desired angular orientation (αdes) with respect to the axis (<NUM>) of rotation in an alternating fashion.