CONTROLLING ROTATIONAL SPEED BY CHANGING BLADE PROFILE

Abstract

Provided is a method of controlling a rotational speed of a rotor of a wind turbine having a rotor with blades connected thereon, at least one blade including a blade profile changing equipment, the method including: changing the blade profile dependent on a rotational speed deviation of an actual rotational speed of the rotor or the generator rotor from a reference rotational speed.

Claims

1. A method of controlling a rotational speed of a rotor of a wind turbine having a rotor with a plurality of blades connected thereon, at least one blade of the plurality of blades including a blade profile changing equipment, the method comprising: changing a blade profile dependent on a rotational speed deviation of an actual rotational speed of the rotor or the generator rotor from a reference rotational speed.

2. The method according to claim 1, wherein changing the blade profile comprises: deriving, using a blade profile controller, a blade profile reference based on the rotational speed deviation; and adjusting the blade profile, using an actuator, based on the blade profile reference.

3. The method according to claim 1, further comprising: determining a setting of the blade profile changing equipment; deriving a blade profile deviation of the blade profile reference from the determined setting of the blade profile changing equipment; supplying a pitch controller input signal to a pitch controller, wherein the pitch controller input signal is based at least on the blade profile deviation; deriving, using the pitch controller, a pitch reference based on the pitch controller input signal; and adjusting a pitch position of the at least one blade based on the pitch reference.

4. The method according to claim 3, wherein the pitch controller input signal is obtained by low pass filtering of the blade profile deviation.

5. The method according to claim 4, further comprising: low pass filtering the determined setting of the blade profile changing equipment; and adding the low pass filtered determined setting of the blade profile changing equipment to the low pass filtered blade profile deviation to obtain the pitch controller input signal.

6. The method according to claim 5, further comprising: deriving a rotational speed deviation rate as a time change of the rotational speed deviation; determining a rate excess of the rotational speed deviation rate over a rate threshold; and adding a low pass filtered determined setting of the blade profile changing equipment, to the low pass filtered blade profile deviation and to the rate excess to obtain the pitch controller input signal.

7. The method according to claim 1, wherein the blade profile changing equipment is mounted at the at least one blade such as to change at least a portion of a surface shape at a suction side of the at least one blade.

8. The method according to claim 1, wherein the blade profile changing equipment comprises an adjustable spoiler, mounted on a suction surface of the at least one blade, the adjustable spoiler being adjustable by supplying a fluid into or withdrawing a fluid out of a cavity or hose thereby adjusting an extent of protrusion of the adjustable spoiler from a surrounding suction surface of the at least one blade.

9. The method according to claim 1, wherein the blade profile changing equipment comprises a flap mounted at the at least one blade, at a rear edge of the at least one blade, the flap extending and defining a rear end portion of a suction side surface.

10. The method according to claim 9, wherein the flap comprises at least a first portion and a second portion which are turnable, relative to each other for changing the blade profile.

11. The method according to claim 9, wherein the setting of the blade profile changing equipment is representable by an relative angle of orientations of the first portion and the second portion of the flap.

12. The method according to claim 1, wherein, during a first time period, a wind speed varies around a first average wind speed and the blade pitch is kept constant at a first blade pitch angle, and, during a second time period, the wind speed varies around a second average wind speed different from the first average wind speed and the blade pitch is kept constant at a second blade pitch angle different from the first blade pitch angle, further wherein during the first time period and the second time period the blade profile is changed, in response to varying wind speed, for keeping the rotational speed of the rotor substantially constant.

13. An arrangement for controlling a rotational speed of a rotor of a wind turbine, having a rotor with a plurality of blades connected thereon, at least one blade including a blade profile changing equipment, the arrangement comprising: a processor configured to control changing the blade profile dependent on a rotational speed deviation of an actual rotational speed of the rotor or the generator rotor from a reference rotational speed.

14. The arrangement according to claim 13, further comprising: a blade profile changing equipment including an actuator communicatively coupled with the processor and being configured to change the blade profile.

15. A wind turbine, comprising: an arrangement according to claim 14; a rotor; and a plurality of blades connected to the rotor, at least one blade including the blade profile changing equipment.

Description

BRIEF DESCRIPTION

[0049] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0050] FIG. 1 schematically illustrates a wind turbine according to an embodiment of the present invention including an arrangement for controlling a rotational speed of a rotor according to an embodiment of the present invention;

[0051] FIG. 2 schematically illustrates a diagram of an arrangement for controlling a rotational speed of a rotor of a wind turbine according to an embodiment of the present invention which may for example be included in the wind turbine illustrated in FIG. 1;

[0052] FIG. 3 illustrates a graph illustrating a pitch angle controller according to a conventional method;

[0053] FIG. 4 illustrates a graph for explaining a combined adjusting of a blade profile changing equipment and a pitch angle according to an embodiment of the present invention, performed by the arrangement illustrated in FIG. 2;

[0054] FIG. 5 schematically illustrates a first embodiment of a blade profile changing equipment according to embodiments of the present invention;

[0055] FIG. 6 schematically illustrates a second embodiment of a blade profile changing equipment according to embodiments of the present invention;

[0056] FIG. 7 schematically illustrates a third embodiment of a blade profile changing equipment according to embodiments of the present invention;

[0057] FIG. 8 schematically illustrates a fourth embodiment of a blade profile changing equipment according to embodiments of the present invention;

[0058] FIG. 9 schematically illustrates a fifth embodiment of a blade profile changing equipment according to embodiments of the present invention; and

[0059] FIG. 10 schematically illustrates a sixth embodiment of a blade profile changing equipment according to embodiments of the present invention.

DETAILED DESCRIPTION

[0060] The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements are provided with the same reference signs or with reference signs, which are different from the corresponding reference signs only within the first digit.

[0061] FIG. 1 schematically illustrates a wind turbine 100 according to an embodiment of the present invention including an arrangement 101 for controlling a rotational speed of a rotor 103 of the wind turbine 100. The wind turbine 100 comprises a rotor 103 at which plural rotor blades 105 are mounted. The wind turbine 100 further comprises an (optional) gearbox 105 which transmits the mechanical rotation of the (primary) shaft 103 to a secondary shaft (also called generator rotor) 107 which partly rotates (in particular having plural permanent magnets attached thereto) in a generator 109. The generator 109 outputs a (in particular three-phase) AC power stream 111 which is supplied to an AC-DC/DC-AC converter 113 which converts the variable frequency power stream 111 to a fixed frequency power stream 115 (in particular three-phase power stream) which is supplied to a wind turbine transformer 117 which transforms the output voltage of the converter to a higher voltage output at the output terminals 119. The wind turbine 100 is connected via a transmission line 121 to a point of common coupling 123 to which plural other wind turbines 125 are connected. The point of common coupling 123 is coupled to a park transformer 127 which provides a high output voltage such as several hundred kV which are transmitted to a utility grid 129.

[0062] The wind turbine 100 comprises for control purposes a controller 102 which harbours in the illustrated embodiment the arrangement 101 for controlling the rotational speed of the rotor 103. In particular, the controller 101 controls, via control signals 104, the converter 113, wherein the control signals 104 may comprise a reference voltage, reference power, reference active power, reference reactive power or the like. The converter 113 may comprise in the AC-DC section as well as in the DC-AC section each for example six power transistors (for three phases) whose gates are driven by gate driver signals comprising pulse width modulation signals as derived from the reference signals 104 supplied to the converter 113.

[0063] The arrangement 101 comprises a processor 106 which is adapted to control changing the blade profile, i.e. the (in particular) aerodynamic profile of the blades 105 dependent on a rotational speed deviation of an actual rotational speed 108 of the rotor 107 (or the rotor 103) from a reference rotational speed which may for example be stored in a storage of the arrangement 101.

[0064] In particular, the actual rotational speed 108 of the secondary shaft 107 is measured using a rotational speed sensor 110 and supplied to the arrangement 101. The arrangement 101 outputs a control signal or drive signal 112 to the blade profile changing equipment 114 which is attached to or mounted to at least one of the rotor blades 105. For changing the blade profile, an actuator may be provided which may be adapted to move at least a portion of the blade profile changing equipment such as to change the aerodynamic profile of the rotor blade 105 in at least one portion thereof, in particular at a suction side 116 of the blade 105. The wind 118 impacts on the pressure side 120 of the rotor blade 105.

[0065] FIG. 2 schematically illustrates an embodiment of an arrangement 201 for controlling a rotational speed of a rotor of a wind turbine in more detail. The arrangement 201 receives the speed measurement signal 208 as well as a reference rotational speed 222 which are supplied to a subtraction element 231 which calculates a rotational speed deviation 233. The rotational speed deviation (also referred to as speed error) is supplied to a blade profile controller 235 (also referred to as flap controller or spoiler controller) which derives therefrom a blade profile reference signal 237. The blade profile reference 237 is supplied to a blade profile changing equipment 239 (for example a flap system or a spoiler adjustment system 114 illustrated in FIG. 1) which thereupon adjusts the blade profile to a particular setting 241 of the blade profile changing equipment. The adjusted setting 241 of the blade profile changing equipment leads to a particular torque or change in torque as effected by the wind impacting on the rotor blade and in turn causes a change in the rotational speed in order to diminish the rotational speed deviation 233.

[0066] In particular wind conditions, it may be sufficient for the wind turbine to control the rotational speed exclusively by adjusting the blade profile using the blade profile changing equipment 114, 239 without requiring to additionally adjust the pitch angle of the blades 105.

[0067] However, under other wind conditions, such as heavily or strongly or rapidly changing wind speed and/or direction, the control method may also involve adjusting the blade pitch angle as is explained below. For these further method steps, the arrangement 201 comprises a further subtraction element 243 which calculates from the actual (e.g. measured) setting 241 of the blade profile changing equipment and from the blade profile reference 237 a blade profile deviation 245 which is provided to a low pass filter 247. The low pass filter 247 dampens or diminishes high frequency variations of the blade profile deviation 245 and the low pass filtered blade profile deviation 245 is provided to an addition element 249.

[0068] To this addition element 249 also, according to embodiments of the present invention, is supplied a low pass filtered version of the setting 241 of the blade profile changing equipment, wherein for low pass filtering, the filter 251 may be used. Threshold frequencies and/or time constants of the filters 247, 251 may be selected or chosen according to the particular application, the constitution of the blade profile changing equipment and so forth.

[0069] The output of the addition element 249 represents a pitch controller input signal 253 which is supplied to a pitch controller 255 which derives based on the pitch controller input signal 253 a pitch reference 257. The pitch reference 257 is provided or supplied to a pitch system 259 which is illustrated in FIG. 1 and labelled with reference sign 159. The pitch system adjusts the pitch angle of the rotor blade by rotation about a longitudinal axis 160 of the rotor blade 105 (oriented in radial direction). Adjusting the pitch angle results in the actual pitch position 261 of the rotor blade which leads to a particular torque and in turn leads to a change in the rotational speed in a direction to diminish the rotational speed deviation 233.

[0070] For addressing rapid and drastic time changes of the rotational speed deviation, the arrangement 201 comprises further a feedforward filter 263 to which the rotational speed deviation 233 is supplied and which outputs a rotational speed deviation rate 265.

[0071] The rotational speed deviation rate 265 is supplied to a saturation block 267 which derives an output 268. When the rotational speed deviation rate 265 is below a threshold as stored in the saturation block 267), then the saturation block 267 outputs as an output signal 268 the rotational speed deviation rate 265. If, however, the rotational speed deviation rate 265 is greater than the threshold stored in the saturation module 267, the saturation module 267 outputs the threshold as the output signal 268.

[0072] The rotational speed deviation rate 265 and the output 268 are supplied to a further difference element 271 which outputs the excess 269 over the output 268 of the saturation element 267. An excess 269, if present, is output by the difference element 271 and supplied to the addition element 249.

[0073] Thereby, the pitch controller input signal 253 may be obtained as a sum of several signals addressing several conditions which may happen during execution of the control method.

[0074] FIG. 3 illustrates a graph showing a wind speed 330 and a pitch angle 332 in dependence of time 334 on the abscissa, wherein on the ordinate 336, the wind speed and the pitch angle, respectively, are indicated. As can be appreciated from FIG. 3, in case of changing wind speed 330, the pitch angle of the wind turbine is controlled according to pitch angle curve 332. Much of the pitch changing activity may, in the conventional system, happen to compensate for small variations in the wind speed.

[0075] These variations are, according to embodiments of the present invention, addressed by actively controlling a blade profile changing equipment, in particular flap and/or a spoiler mounted at the blades. This is illustrated in FIG. 4 which shows on an abscissa 434 the time and on an ordinate 436 the wind speed, the pitch angle and a setting of a blade profile changing equipment according to an embodiment of the present invention. In particular, the pitch angle is illustrated as a curve 438, the setting of the blade profile changing equipment is labelled with reference sign 440 and the wind speed is labelled with reference sign 442. In the graph illustrated in FIG. 4, in fact the setting 440 of the blade profile changing equipment is represented by a flap angle of a flap mounted at a (rear end of a) rotor blade. Controlling the flaps of the blade effectively changes the aerodynamic profile of the blade.

[0076] While the wind speed stays (on average) at a particular level, the pitch angle may be kept constant, i.e. no pitching is needed. This can be appreciated from FIG. 4 where the pitch angle stays at a first pitch angle while the wind speed 442 varies around a first wind speed average. When the wind speed 442 varies around a second wind speed average, the pitch angle is adjusted to a second pitch angle different from the first pitch angle. By diminishing the pitching, the blade bearing may not be worn out.

[0077] Whenever a large change in the wind speed happens as for example time point 444, the pitch controller 255 may pitch the blade into a new equilibrium position and the blade profile changing equipment (in particular the flaps) may once again handle all the small variations in the wind speed around this new equilibrium. The flap angle (curve 440) varies before and after the change of the wind speed at time point 444 in about a same extent around a mean value 441.

[0078] As an advantage of the control method according to embodiments of the present invention, a large reduction in the traveled distance of the blade bearings due to small variations in the wind speed may be achieved.

[0079] Conventionally, for all small variations in the wind speed, pitching is performed, leading to wear out of the pitch bearings. The reduction in traveled blade bearing distance according to embodiments of the invention may mean less wear on the bearings and less blade bearing warranty cases, exchanges, longer service intervals, etc.

[0080] Under the term blade profile it is also understood to adjust a drag, for example established by an adjustable spoiler. Thus, instead of using one or more flaps on the rotor blade, also one or more spoilers on particular the suction surface of the rotor blade may be utilized, to change the blade profile. This has been conventionally also referred to as drag. There may be various ways to increase or decrease the drag of the rotor blade. One is to use a spoiler, another is to generate stall which both may reduce lift and increase drag. One advantage of using drag to control power is that drag goes almost directly to rotor torque and hence power.

[0081] In the FIGS. 5 to 10, different configurations of blade profile changing equipment are illustrated, according to embodiments of the present invention.

[0082] FIG. 5 schematically illustrates an embodiment of a blade profile changing equipment 514 here embodied as a movable trailing edge arrangement. In the attachment region (also referred to as first portion) 563, the equipment 514 may be attached to a trailing edge section of a rotor blade 105. The equipment 514 further comprises an aerodynamic changing portion (also referred to as second portion) 565 which is shaped as a flap. The aerodynamic portion 565 of the movable trailing edge arrangement 514 is detachably connected with the remaining part of the equipment 514. The equipment 514 comprises an inflatable and deflatable hose or bag 567 which can for example be inflated by providing compressed air or fluid into an inside of the hose 567.

[0083] The deflated state is illustrated in the view 524 and the inflated configuration is illustrated in the view 526 of FIG. 5. Upon inflation of the hose 567, the portions 563 and 565 change their relative orientation and a region between the regions 563 and 565 comprises a bent portion 569. The angle between upper surfaces of the portions 563 and 565 may for example characterize a setting of the blade profile changing equipment 514.

[0084] FIG. 6 illustrates schematically another embodiment of a flap 614 as mounted on a rear end portion 671 of a blade 605. In the view 624, a flexible hose or bag 667 is inflated causing a rear end portion 665 of the flap 614 to turn upwards. In the non-inflated situation illustrated in view 626, the rear end portion 665 of the flap 614 is turned downwards relative to the view 624, thereby changing the blade profile.

[0085] FIG. 7 illustrates different orientations of flaps 714 having rear end portions 765. The change of the orientation of the rear end portions 765 may be effected by filling a liquid or compressed air into a cavity or a hose or actuating an electric motor, for example, or using a hydraulic system.

[0086] FIGS. 8 and 9 illustrate in an overview (FIG. 8) and in a detailed view (FIG. 9) a spoiler 814 as another example of a blade profile changing equipment according to embodiments of the present invention. Thereby, the view 824 illustrates the spoiler in a non-inflated configuration, while the view 826 illustrates the spoiler 814 in an inflated configuration. Wind trajectories 828 are depicted illustrating an enhanced drag effect, when the spoiler 814 is in the inflated configuration as illustrated in the view 826.

[0087] FIG. 10 schematically illustrates another example of a blade profile changing equipment 1014 in a deflated configuration in view 1024 and in an inflated configuration in view 1026. The equipment 1014 comprises a cavity 1030 which may be filled with a fluid, in particular compressed air, to switch from the deflated configuration illustrated in view 1024 to the inflated configuration illustrated in view 1026. Upon inflation of the cavity 1030, a connected portion 1065 changes its orientation from an extended or protruding configuration in view 1024 to a buried or hidden configuration in view 1026, thereby changing the blade profile.

[0088] Other configurations of the blade profile changing equipment are possible.

[0089] It should be noted that the term comprising does not exclude other elements or steps and a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.