Method for controlling a wind turbine

Abstract

A method for operating a wind turbine, and the wind turbine has an aerodynamic rotor with a rotor hub and with rotor blades of which the blade angle can be adjusted, and the aerodynamic rotor can be adjusted in respect of its azimuth direction, and the method comprises the steps of detecting a storm situation in which the prevailing wind is so strong that the wind turbine is moved to a coasting mode for self-protection purposes, orienting the rotor in respect of its azimuth position into a low-loading orientation in relation to the wind, in which orientation the wind turbine is subjected to as little loading as possible by the wind from a main wind direction, detecting at least one loading (L.sub.M) which is caused by a gust of wind and acts on the rotor, and adjusting at least one of the rotor blades in respect of its blade angle such that the at least one rotor blade is subjected to as little loading as possible by the causative gust of wind.

Claims

1. A method for operating a wind turbine, the wind turbine having an aerodynamic rotor with a rotor hub and a plurality of rotor blades with adjustable blade angles, wherein an azimuth position of the aerodynamic rotor is adjustable, the method comprising: detecting a storm situation in which a prevailing wind is so strong the wind turbine is moved to a coasting mode for self-protection purposes; orienting the azimuth position of the rotor into a low-loading orientation relative to the wind such that the wind turbine is subjected to as little loading as possible by the wind from a main wind direction; detecting at least one loading caused by a gust of wind acting on the rotor; and adjusting a blade angle of at least one of the plurality of rotor blades such that the at least one rotor blade is subjected to minimal loading by the causative gust of wind, wherein adjusting the at least one rotor blade is performed in response to the causative gust of wind having a wind speed that is greater than an average wind speed of the prevailing wind by a predetermined wind speed difference.

2. The method as claimed in claim 1, wherein adjusting comprises adjusting the at least one rotor blade depending on a detected blade loading, wherein the method further comprises entering the at least one loading detected into a load control arrangement, and wherein the load control arrangement adjusts the blade angle of the rotor blade depending on the detected loading such that the loading is minimized.

3. The method as claimed in claim 1, wherein: at least one load sensor is provided on the rotor blade or in a region of a fastening of the rotor blade to the rotor hub for each rotor blade, and a load signal is fed from the at least one load sensor to a control apparatus of the rotor blade to carry out the adjustment of the rotor blade angle.

4. The method as claimed in claim 1, further comprising: moving the plurality of rotor blades to a feathered position; and starting from the feathered position, adjusting the blade angle of each rotor blade individually about an angle deviation in relation to the feathered position.

5. The method as claimed in claim 1, wherein: the causative gust of wind has a wind speed that is greater than a predetermined limit gust of wind speed, or the causative gust of wind has a gust of wind direction that deviates from the main wind direction with respect to magnitude by a predetermined wind direction difference.

6. The method as claimed in claim 1, wherein the low-loading orientation is an orientation that faces the main wind direction.

7. The method as claimed in claim 1, wherein the gust of wind is detected with respect to wind speed and wind direction.

8. The method as claimed in claim 1, wherein each rotor blade of the plurality of rotor blades are configured to be adjusted to greater and smaller blade angles than a feathered position.

9. The method as claimed in claim 1, wherein a once-every-50-years storm situation or a once-a-year storm situation is taken into account prior to adjusting the blade angle.

10. A wind turbine configured to execute the method as claimed in claim 1.

11. A wind turbine comprising: an aerodynamic rotor with a plurality of rotor blades, wherein the blade angles of the plurality of rotor blades are adjustable, wherein an azimuth position of the aerodynamic rotor is adjustable; and a programmed process computer configured to execute a method comprising: detecting a storm situation in which a prevailing wind is so strong that the wind turbine is moved to a coasting mode for self-protection purposes; orienting the azimuth position of the rotor into a low-loading orientation relative to the wind such that wind on the wind turbine from a main wind direction is minimized; detecting at least one gust of wind acting in a region of the aerodynamic rotor; and in response to the at least one gust of wind having a wind speed that is greater than an average wind speed of the prevailing wind by a predetermined wind speed difference, adjusting a blade angle of at least one of the plurality of rotor blades in respect of its blade angle such that the at least one rotor blade is subjected to minimal loading by the gust of wind detected.

12. The wind turbine as claimed in claim 11 further comprising: at least one load sensor on the at least one rotor blade or in a region of a fastening of the rotor blade to a rotor hub for the at least one rotor blade, a control apparatus, and a signal transmission device configured to feed back a load signal from the at least one load sensor to the control apparatus to cause the adjustment of the at least one rotor blade depending on the load signal to minimize or at least to reduce a loading that is detected by the load signal.

13. The wind turbine as claimed in claim 12, further comprising: blade adjustment devices coupled to the plurality of rotor blades, the blade adjustment devices being configured to adjust the blade angle of the respective rotor blade, and control apparatuses coupled to the plurality of rotor blades, the control apparatuses being configured to implement the adjustment of the blade angle of the at least one rotor blade, wherein the control apparatus is configured to receive the load signal from the at least one load sensor and to control the respective blade adjustment device depending on the signal to implement the adjustment of the at least one blade angle to minimize or at least to reduce the loading that is detected by the load signal.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will be explained in more detail below by way of example using embodiments with reference to the accompanying figures.

(2) FIG. 1 shows a perspective illustration of a wind turbine.

(3) FIG. 2 schematically shows a control diagram for implementing the load-relieving mode.

(4) FIG. 3 schematically shows a basic outline of a detail of a blade connection region.

(5) FIG. 4 shows a simplified flowchart particularly for activating a load-relieving mode.

DETAILED DESCRIPTION

(6) FIG. 1 shows a wind turbine 100 having a tower 102 and a nacelle 104. A rotor 106 comprising three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. The rotor 106 is made to execute a rotational movement by the wind during operation and thereby drives a generator in the nacelle 104.

(7) FIG. 2 shows, in an illustrative manner, a control structure 200 which controls the blade angle of the likewise schematically illustrated rotor blade 202 for implementing a load-relieving mode. A rotor blade longitudinal axis 204 is schematically drawn as a dashed-and-dotted line in the rotor blade 202 and a chord 206 is drawn as a dashed line in a middle region of the rotor blade 202 likewise in a highly schematic manner. A load sensor 208 is likewise indicated in the root region 210 of the rotor blade 202.

(8) The load sensor 208 is arranged, for instance, such that it receives a loading which also corresponds to a bending movement 212 of the rotor blade 202 substantially perpendicular to the chord 206. Therefore, here, said bending movement is a bending movement about an axis which runs substantially parallel to the chord 206. In other words, said bending movement is a bending movement or corresponding load direction for instance in the direction of an intake side to a delivery side or vice versa and not a direction between a front edge 214 and a rear edge 216. The intake side and delivery side cannot be very clearly illustrated in the schematic illustration of FIG. 2, and therefore reference is made to the front edge 214 and rear edge 216 for the purpose of drawing a distinction here.

(9) A loading in a direction of this kind, that is to say which corresponds to the bending movement 212 according to the double-headed arrow drawn, is received by the load sensor 208. The load sensor 208 generates a corresponding load signal, this being illustrated here as L.sub.M and being subtracted from a load setpoint value L.sub.S at the summing point 218. The setpoint value L.sub.S can preferably have the value 0.

(10) This setpoint value/actual value difference, which can also be denoted e, is then entered into the PI control block 220. A PI controller is proposed particularly so that a blade adjustment, which has led to a minimization of the loading and therefore of the load signal L.sub.M, is maintained even when the control deviation e has the value 0. However, other controllers can also be used or a further component, such as a D component for example, can also be added for example in order to optionally influence the control dynamics.

(11) The result of the PI control block 220 is then passed to the illustrative pitch block 222 which interacts with the likewise only schematically illustrated pitch drive 224. The pitch block 222 and the pitch drive 224 can form a blade adjustment device or a part thereof. The pitch drive 224 then carries out an adjustment of the blade angle by way of an indicated pinion 226, specifically a rotation essentially around the rotor blade longitudinal axis 204 if a corresponding adjustment signal has actually been generated by the PI control block 220.

(12) FIG. 3 illustrates, in the schematic sectional illustration of a rotor blade connection region 300, a possible structural arrangement of the schematic diagram of FIG. 2. The blade connection region 300 according to the illustration of FIG. 3 comprises a root region 310 of a rotor blade which could correspond to the rotor blade 202 of FIG. 2. Said root region 310 is rotatably mounted in a pitch bearing 330 in a hub section 332. The rotor blade longitudinal axis 304 is likewise drawn for illustration purposes.

(13) In order to detect a loading, a load sensor 308 in the form of a strain gauge is drawn in an illustrative manner in the root region 310. The shown orders of magnitude of the elements, particularly of the load sensor 308, with the same applying for the load sensor 208 of FIG. 2 as well, do not have to correspond to actual orders of magnitude and have been selected substantially for the purpose of clear illustration.

(14) The load sensor 308 can detect a load signal L.sub.M and transmit said load signal to a control apparatus 334. Here, the control apparatus 334 is illustrated as a microprocessor and can contain a part of the structure of FIG. 2, particularly the summing point 218 illustrated there and the PI control block 220. The pitch block 222 could also be part of the control apparatus 334.

(15) The control apparatus 334 can then actuate the pitch drive 324, which is schematically illustrated as a motor here. Any adjustment specifications can then be implemented by means of a pinion 326 which is likewise merely indicated. An adjustment of the rotor blade angle by means of a mechanism other than by means of a pitch drive with a pinion is of course possible too. FIG. 3 illustrates that the control apparatus 334 can be arranged in the region of the rotor blade, particularly in the blade connection region 300. Therefore, a control apparatus 334 of this kind is also provided for each rotor blade and therefore a corresponding control operation, in particular implementation of the load-relieving mode, can be carried out for each rotor blade individually in a simple manner.

(16) The schematic process structure 400 of FIG. 4 proceeds, in principle, from a normal mode of the wind turbine. This is illustrated by the normal block 440. Starting from said normal block, a check is made in the storm checking block 442 as to whether the wind speed V is greater than a storm wind speed V.sub.S. If this is not the case, the normal mode is continued and the process accordingly returns to the normal block 440.

(17) However, if it is identified that the wind speed is correspondingly high, the operation management, which is also shown in this process structure 400 in this respect, moves to the storm operating mode which is illustrated by the storm block 444 here. It should be noted that this storm operating mode, which is illustrated by the storm block 444, does not refer to the storm situation in which the wind turbine is operated further at reduced power and/or reduced rotation speed but rather in which the wind turbine is not operated further and moves to a coasting mode. The management of the wind turbine in the coasting mode is therefore a characteristic of the storm situation under consideration here which is represented by the storm block 444.

(18) Furthermore, according to the process structure 400, a check is then made in the gust of wind limit block 446 as to whether a gust of wind B is greater than a gust of wind limit B.sub.G. This can mean that a wind speed of the gust of wind is compared with a predetermined limit wind speed of a gust of wind and/or a comparison of a wind speed increase in the gust of wind in relation to a prevailing average wind speed is performed with a predetermined limit value and/or that a wind direction of the gust of wind, which wind direction differs from the prevailing main wind direction, is observed and this wind direction deviation is compared with a predetermined wind direction deviation limit.

(19) If the result of this comparison is that the gust of wind B is not greater than a gust of wind limit, the storm mode continues in a fundamentally unchanged manner. Therefore, the structure returns from the gust of wind limit block 446 to the storm block 444 in this situation.

(20) However, if it has been identified in the gust of wind limit block 446 that a gust of wind is greater than a gust of wind limit, a load-relieving mode is additionally activated. This is represented by the idle block 448. In this load-relieving mode according to the idle block 448, a control operation is then activated, as is schematically shown in FIG. 2 for example. In other words, according to this process structure 400, said control operation according to FIG. 2 is activated only when this is triggered by the gust of wind limit block 446. Therefore, in the storm mode according to the storm block 444, the control operation according to FIG. 2 is preferably not yet active in the manner shown there.

(21) It should be noted that the check according to the storm checking block 442 and also the check according to the gust of wind limit block 446 continue to be carried out. Therefore, the check according to the gust of wind limit block 446 also continues to be performed in the activated load-relieving mode 448 and accordingly the load-relieving mode may be deactivated again. A check according to the gust of wind limit block 446 is preferably then carried out such that the load-relieving mode is deactivated only when a situation in which the gust of wind B was not greater than the gust of wind limit B.sub.G has not occurred for a relatively long time, for example for a time of at least 10 minutes or for a time of at least one hour.

(22) Similarly, a check in the sense of the storm checking block 442 can be performed in the storm mode and the process can optionally be returned to the normal mode.

(23) The described invention relates particularly to the control of a wind turbine at high wind speeds. It is known that a wind turbine stops the normal production mode at high wind speeds and changes over to the coasting mode. In the process, the rotor blades, which can also be called blades for reasons of simplicity, are rotated out of the wind into a so-called feathered position so that said rotor blades do not draw any energy or draw only very little energy from the incident air. A turbine in the feathered position does not rotate or rotates only slightly. This is called coasting or the coasting mode here.

(24) It has been found that, owing to the high level of turbulence in the wind, the situation that the wind or individual gusts of wind do not act on the turbine in an ideal manner from the front can arise in the process. Owing to these gusts of wind, the turbine is then no longer in the feathered position and energy is drawn from the wind. This drawn energy results in increased loads on the turbine.

(25) The proposed solution makes provision here for the feathered position to be accordingly adapted by controlling the blade load signal by way of the load signal being adjusted to zero, particularly by means of a PI controller. This can be done separately or individually for all blades. The respectively optimal blade angle, which can differ significantly from the normal feathered position at 90°, is determined by the control operation.

(26) The control operation therefore leads to sometimes severely reduced blade connection loads in storm conditions. The loads which occur in storm conditions can have a determinative effect on the dimensions, so that a load reduction may also result in potential cost reductions due to reduced component loads. Therefore, the design of the turbine can be influenced as a result of this or this can be taken into account at the design stage.

(27) In addition to developing and implementing the proposed algorithm, one refinement also proposes adapting any blade angle stops. The blade angles, which can also be called pitch angles, are normally limited to values close to 90°. However, with the solution proposed now, pitch angles >90° can prove to be advantageous, so that structural changes to the blade adjustment system, which can contain a blade adjustment device and an angle monitoring arrangement, may be proposed.

(28) It has also been found that gusts of wind which occur in storm conditions do not necessarily follow the main wind direction, and therefore these gusts of wind flow against the blades with a strong oblique incident flow. This generates more lift on the blade than the incident flow in the feathered position, and therefore results in higher blade loads.

(29) To this end, a gust of wind identification arrangement is preferably implemented, this activating the load-relieving mode as required. This then particularly preferably adjusts the blade angle down to minimal blade impact loads with the aid of a PI controller. This leads to a correction of the blade angles deviating from the feathered position.

(30) As a result, greatly reduced blade connection loads can be produced. These can also reduce the extreme loads. Load situations of this kind can also be determinative for the dimensions in turbines, and therefore a reduction of this kind can have a direct influence on the construction or be taken into account during the construction here.