WIND TURBINE OPERATIONAL METHOD FOR RESPONDING TO GRID DISTURBANCE

Abstract

It is described a method of operating at least one adaptable airflow regulating system (13) of at least one rotor blade (15) of a wind turbine (1) connected to a utility grid (6), the method comprising: receiving information (10) regarding a grid disturbance; adapting, in particular during a disturbance duration, the airflow regulating system (13) based on the information (10), while the wind turbine (1) stays connected to the utility grid (6).

Claims

1. A method of operating at least one adaptable airflow regulating system of at least one rotor blade of a wind turbine connected to a utility grid, the method comprising: receiving information regarding a grid disturbance; adapting, during a disturbance duration, the at least one adaptable airflow regulating system based on the information, while the wind turbine stays connected to the utility grid, wherein controlling the at least one adaptable airflow regulating system comprises: moving a position and/or an orientation of at least one aerodynamically active surface of the at least one adaptable airflow regulating system relative to an airfoil portion of the at least one rotor blade.

2. The method according to claim 1, wherein the grid disturbance comprises a grid voltage drop of a grid voltage, the grid voltage drop reducing the grid voltage to between 0% and 50% of a nominal grid voltage, for a duration between 0.1 s and 10 s, further wherein adapting the airflow regulating system is performed, only if the grid voltage drop is greater than a threshold.

3. The method according to claim 1, wherein wherein an aerodynamic lift of the at least one rotor blade and/or an aerodynamic torque is, due to an adaptation of the at least one adaptable airflow regulating system, reduced more the bigger a grid voltage drop.

4. The method according to claim 1, wherein adapting the at least one adaptable airflow regulating system comprises reducing an aerodynamic lift of the at least one rotor blade land/or an aerodynamic torque acting on a rotor to which at least one rotor blade is mounted by between 10% and 70% of a lift or a torque, respectively, prior to the grid disturbance, within a time span between 0.1 s and 3 s.

5. The method according to claim 1, wherein adapting the at least one adaptable airflow regulating system comprises adjusting a setting that depends on at least one of: at least one operating parameters of the wind turbine; at least one external condition; at least one property of the grid disturbance, the external conditions comprising at least one of: wind velocity, and wind turbulence; and the operating parameters comprising at least one of: pitch angle of the rotor blade; rotational speed of the rotor; and power output.

6. The method according to claim 1, wherein adapting the at least one adaptable airflow regulating system is further based on an operating point of the wind turbine, and at a first operating point where a setting change of the airflow regulating system has more impact on a lift of the at least one rotor blade, a setting of the at least one adaptable airflow regulating system is changed to a smaller degree than at a second operating point where a setting change has less impact on the lift of the at least one rotor blade.

7. The method according to claim 1, further comprising at least for a part of a disturbance duration: keeping a pitch angle of the at least one rotor blade at least substantially unchanged; or the method further comprising, within a disturbance duration: changing a pitch angle of the at least one rotor blade based on the information to reduce a lift of the at least one rotor blade.

8. The method according to claim 1, wherein, if the grid does not return to normal operation within a predetermined threshold time range, the method comprises: stopping the wind turbine by: adapting the at least one adaptable airflow regulating system such that a maximum airflow stall is effected; and/or pitching out the at least one rotor blade; and/or breaking a rotor.

9. The method according to claim 1, wherein, after the grid disturbance the grid restores to a nominal grid status which has a nominal grid voltage, the method comprises: adapting the at least one adaptable airflow regulating system to increase lift of the at least one rotor blade to a pre-disturbance lift as was present prior to the grid disturbance, based on at least one of: a grid disturbance duration, a rate at which a pre-disturbance power output is re-established, a rotor speed, and a pitch angle.

10. The method according to claim 9, wherein adapting the at least one adaptable airflow regulating system to a pre-disturbance lift is performed within a time span of between 0.1 s and 3 s.

11. The method according to claim 1, wherein receiving information regarding the grid disturbance comprises: detecting the grid disturbance; and deriving the information based on the detected grid disturbance.

12. The method according to claim 1, wherein the at least one adaptable airflow regulating system comprises at least one of: a flap arranged at a trailing edge of the at least one rotor blade a segmented, spoiler arranged at a suction surface of the at least one rotor blade, wherein the at least one adaptable airflow regulating system is different from a pitch angle changing system.

13. An arrangement for operating at least one adaptable airflow regulating system of at least one rotor blade of a wind turbine connected to a utility grid in case of a grid disturbance, the arrangement comprising: a processor adapted to derive a control signal based on the information regarding the grid disturbance in order to adapt, during a disturbance duration, the at least one adaptable airflow regulating system, wherein adapting the at least one adaptable airflow regulating system comprises: moving a position and/or an orientation of at least one aerodynamically active surface of the at east one adaptable airflow regulating system relative to an airfoil portion of the least one rotor blade.

14. A wind turbine, comprising: a wind turbine nacelle; a rotor shaft harboured in the nacelle, at which the rotor shaft a plurality of rotor blades are mounted, at least one rotor blade having at least one adaptable airflow regulating system; and the arrangement according to claim 13 connected to control the at least one adaptable airflow regulating system.

Description

BRIEF DESCRIPTION

[0053] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0054] FIG. 1 schematically illustrates a wind turbine according to an embodiment of the present invention comprising an arrangement according to an embodiment of the present invention; and

[0055] FIG. 2 illustrates a method scheme of operating at least one adaptable airflow regulating system of at least one rotor blade of a wind turbine connected to a utility grid, in case of a grid disturbance, as e.g. performable by the arrangement illustrated in FIG. 1.

DETAILED DESCRIPTION

[0056] The illustration in the drawings is in schematic form.

[0057] The wind turbine 1 schematically illustrated in FIG. 1 comprises a wind turbine tower 3 which is erected at a not illustrated base. The wind turbine further comprises a nacelle 5 which is rotatably mounted on top of the wind turbine tower 3. The wind turbine nacelle 5 comprises a rotor shaft 7 (having an axis 8) which is installed within the nacelle 5. The rotor shaft drives a generator 9 which generates electric energy which is supplied to a converter 11 which converts the variable frequency AC power stream to a substantially fixed frequency power stream which is provided to a wind turbine transformer which transforms the output voltage to a higher value.

[0058] The wind turbine 1 further comprises an arrangement 20 of controlling at least one adaptable airflow regulating system 13 which is provided at at least one wind turbine blade 15. Therein, the rotation shaft 7 has a hub 17 at which plural rotor blades 15 (having blade tip 25) are mounted, via blade root 12. At least one rotor blade has a flow regulating system 13.

[0059] In the illustrated embodiment, the flow regulating system comprises a segmented spoiler having spoiler segments 19a, 19b, 19c, 19d, 19e, 19f which are arranged on a suction side 14 along a longitudinal axis 21 of the rotor blade 15. The airflow regulating system 13 may further comprise at least one flap at a trailing edge 16, wherein flaps are indicated with reference sign 23.

[0060] The arrangement 20 is adapted to control the adaptable airflow regulating system 13. Thereby, the arrangement 20 performs a method 30 as is illustrated in FIG. 2. In a method step 31, information is received regarding a grid disturbance. Therein, the information may for example be received from an operator of the utility grid 6, wherein the information is denominated in FIG. 1 with reference sign 10 as received via a signal line 41 by the arrangement 20.

[0061] The arrangement 20 illustrated in FIG. 1 comprises a not illustrated processor which is configured to perform a method of regulating or adapting the airflow regulating system 13 according to an embodiment of the present invention. In a method step 33, the airflow regulating system (for example system 13 in FIG. 1) is adapted (or adjusted or set in a particular state) based on the information 10, while the wind turbine stays connected to the utility grid. Thus, the wind turbine 1 provides AC power output 18 via a power line 22 to the utility grid 6.

[0062] The arrangement 20 may for example be arranged within the hub 17 of the wind turbine or may be arranged within the nacelle 5 depending on the application.

[0063] The arrangement 20 then controls the flow regulating system 19a, 19b, 19c, 19d, 19e, 19f and/or 23 by supplying appropriate control signals, for example via a control line 47 to the individual segments 19a, . . . , 19f and control lines 48 to flaps 23. These segments 19a-19f may then individually turned on or off, for example if they comprise two distinguished or discrete states. In other embodiments, additionally or alternatively, a continuous adaptation of the flow regulating device 13 may be performed, for example by continuously moving an orientation and/or position of the trailing edge flaps 23. By controlling the airflow regulating system 13 by the arrangement 20, an appropriate reaction or response to a disturbance in the utility grid 6 may be achieved.

[0064] Each of the spoiler segments 19a, . . . , 19s has a respective aerodynamically active surface which is exposed to the airflow around or across (suction side 14 of) the rotor blade 15. This active surface is moved regarding position and/or orientation due to the control signals supplied from the arrangement 20. For example, in an on-state, the active surface may be flipped out to a particular degree, for example using an inflated hose arranged below the active surface. In an off-state for example, the active surface may be flipped in such that the surface is completely retracted, to not disturb or influence an airflow across the suction side surface 14 of the rotor blade 15.

[0065] Embodiments of the present invention utilize active blade add-ons to unload the rotor of the wind turbine whenever a grid event is detected that may require reduction of the generator torque or which will reduce the generator torque.

[0066] The conventionally used pitch system for adapting the lift of the rotor blades may be relatively slow compared to an airflow regulating system installed at or on the rotor blade surface. Generally, time constants of pitching systems may be larger which make larger turbines become prone to such events as a grid drop.

[0067] Active blade add-ons, such as airflow regulating system 13, including spoiler(s) and/or trailing edge flaps may make a significant change to the lifting force of the rotor in a very short time. Therefore, the effect of a grid drop can be compensated faster than by applying a pitching regulation, especially if the pitching system has limited capabilities (or can be made cheaper not to have such high demands). Similarly, the lift change, i.e. the aerodynamic change of the lifting force effected by the rotor blade, can be quickly negated after the fault, to re-establish full power production.

[0068] The utility grid 6 has a nominal grid voltage. During a grid disturbance, the voltage may drop considerably, for example between 0% and 100% of a nominal grid voltage. Methods according to embodiments of the present invention may handle a situation when the voltage drop is for example between 0% and 50% of a nominal grid voltage. By operating the airflow regulating system 13, the lifting force may be reduced for example by between 10% and 70% of the lift prior to the grid disturbance.

[0069] The wind turbine 1 further comprises a not in detail illustrated pitching system 40 which is capable of changing the pitch angle of each of the rotor blades 15, i.e. setting a particular rotational angle a around the longitudinal axis 21 of the respective rotor blade 15. According to embodiments of the present invention, only the airflow regulating system 13 is adapted but not the pitching system 40 is activated in order to respond to a grid disturbance.

[0070] In other embodiments, both the airflow regulating system 13 is adapted as well as the pitching system 40 is activated in order to set the rotor blade including the airflow regulating system 13 into a state, where the lifting force is considerably reduced, in dependence of the severity of the grid disturbance and other operational parameters of the wind turbine.

[0071] In the following, particular implementations of a method according to embodiments is described, to which embodiments of the invention is however not limited: [0072] 1) Detect a grid fault. [0073] 2) Apply active blade add-ons (to remove lift from the rotor blade) to unload the turbine rotor 7 [0074] the action from active blade add-ons may happen in addition or instead of pitching. [0075] The action from active blade add-ons may be scheduled by gain scheduling such that the impact is adjusted to the operating point, e.g. apply smaller change at operating points where the add-on has a higher impact (gain) on the lift/torque/thrust of the rotor or the aerodynamics of the rotor. [0076] 3) Remove the action from the blade add-ons if the grid returns to normal operation [0077] the removal of the blade add-ons action may be scheduled based on grid fault duration, the rate that the power is re-established, rotor speed and pitch angle [0078] if the grid does not return to normal operation, then the turbine will stop and action for the blade add-ons can be removed.

[0079] Embodiments of the present invention may provide the following advantages: [0080] The grid drop load case can be design-driven and may cause added cost to the wind turbine, because the wind turbine needs either to be able to pitch faster following a grid voltage drop or withstand the additional extreme loads resulting from the grid disturbance event. Introducing a handle to reduce the impact of the grid drop may lead to a cheaper design with less loading. [0081] The likelihood of driving the turbine into an overspeed event, i.e. rotor overspeed event, or expose it to ultimate loads, following a grid drop may be reduced by this additional control handle to adapt the airflow regulating system. [0082] Costs may be reduced because the hydraulic or electrical pitch system capabilities may be reduced. [0083] Improved ability to produce cost-competitive wind turbines. [0084] Improved capability to fulfil strict grid codes requirements on re-establishing of power production.

[0085] Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0086] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.