METHOD OF CONTROLLING A WIND TURBINE AND CONTROLLER FOR A WIND TURBINE

Abstract

A method of controlling a wind turbine, wherein a minimum required hydraulic pressure represents a hydraulic pressure of at least one accumulator of the wind turbine which is required to pitch at least one blade of the wind turbine which is associated with the accumulator into a stop position of the wind turbine, and wherein a pitch angle represents a pitch angle of a normal of the at least one blade of the wind turbine relative to an incoming wind direction. The method includes (a) determining a minimum requirement function of the minimum required hydraulic pressure dependent on the pitch angle, (b) detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade, and (c) controlling the wind turbine such that the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle.

Claims

1. A method of controlling a wind turbine, wherein a minimum required hydraulic pressure represents a hydraulic pressure of at least one accumulator of the wind turbine which is required to pitch at least one blade of the wind turbine which is associated with the at least one accumulator into a stop position of the wind turbine, wherein a pitch angle represents a pitch angle of a normal of the at least one blade of the wind turbine relative to an incoming wind direction, the method comprising: determining a minimum requirement function of the minimum required hydraulic pressure dependent on the pitch angle, detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade; and controlling the wind turbine such that the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle.

2. The method according to claim 1, further comprising: determining an offset minimum requirement function being offset to the minimum requirement function by a predetermined positive offset and representing a function of an offset minimum required hydraulic pressure dependent on the pitch angle; detecting the current hydraulic pressure in the at least one accumulator at the current pitch angle of the at least one blade; determining that current hydraulic pressure is higher than the minimum required hydraulic pressure at the current pitch angle and lower than the offset minimum required hydraulic pressure at the current pitch angle; and controlling the wind turbine such that the current hydraulic pressure is above the offset minimum required hydraulic pressure at the current pitch angle.

3. The method according to claim 1, wherein the minimum requirement function is determined by a section-wise linear interpolation and/or a section-wise exponential interpolation.

4. The method according to claim 2, wherein a distance between the minimum requirement function and the offset minimum requirement function is constant along the pitch angle.

5. The method according to claim 2, wherein the controlling comprises an adapting of a pitch adjustment speed of at least one blade of the wind turbine.

6. The method according to claim 5, wherein the adapting of the pitch adjustment speed comprises an adapting of the pitch adjustment speed towards a stop position of at least one blade of the wind turbine and/or an adapting of the pitch adjustment speed towards an operation position of the at least one blade of the wind turbine.

7. The method according to claim 5, wherein the adapting of the pitch adjustment speed defines the pitch adjustment speed dependent on the current hydraulic pressure.

8. The method according to claim 7, wherein the pitch adjustment speed dependent on the current hydraulic pressure is changed linearly or exponentially.

9. The method according to claim 5, wherein towards an operation position of the at least one blade of the wind turbine, the pitch adjustment speed changes dependent on the current hydraulic pressure from 100% at the offset minimum required hydraulic pressure to 0% at the minimum required hydraulic pressure.

10. The method according to claim 5, wherein towards a stop position of the at least one blade of the wind turbine, the pitch adjustment speed changes dependent on the current hydraulic pressure from 50% at the offset minimum required hydraulic pressure to 0% at the minimum required hydraulic pressure.

11. A controller for a wind turbine wherein a minimum required hydraulic pressure represents a hydraulic pressure of at least one accumulator of the wind turbine which is required to pitch at least one blade of the wind turbine which is associated with the at least one accumulator into a stop position of the wind turbine, wherein a pitch angle represents a pitch angle of a normal of the at least one blade of the wind turbine relative to an incoming wind direction, the controller comprising: a determining device for determining a minimum requirement function determining minimum pressure values of the minimum required hydraulic pressure dependent on the pitch angle; a detecting device for detecting a current hydraulic pressure in the at least one accumulator at a current pitch angle of the at least one blade; and a controlling device for controlling the wind turbine such that the current hydraulic pressure is above the minimum required hydraulic pressure at the current pitch angle.

Description

BRIEF DESCRIPTION

[0058] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0059] FIG. 1 shows a schematic section of a wind turbine to which the method of controlling and the controller of the present invention may be applied for controlling the wind turbine;

[0060] FIG. 2 shows a graph illustrating how controlling of the wind turbine according to an embodiment of the present invention is operated;

[0061] FIG. 3 shows a graph illustrating how controlling of the wind turbine according to an embodiment of the present invention may prevent a shutdown of the wind turbine′

[0062] FIG. 4 shows a graph illustrating how controlling of the wind turbine according to a further embodiment of the present invention is operated;

[0063] FIG. 5 shows a graph illustrating how adapting of the pitch adjustment speed according to an embodiment of the present invention is operated;

[0064] FIG. 6 shows a graph illustrating how adapting of the pitch adjustment speed according to a further embodiment of the present invention is operated;

[0065] FIG. 7 shows a graph illustrating how controlling of the wind turbine according to a further embodiment of the present invention may prevent a shutdown of the wind turbine;

[0066] FIG. 8 shows a graph illustrating how controlling of the wind turbine according to a further embodiment of the present invention may prevent a shutdown of the wind turbine.

DETAILED DESCRIPTION

[0067] The illustration in the drawings is schematic. It is noted that in different figures, similar or identical elements or features are provided with the same reference signs or with reference signs, which are different from the corresponding reference signs only within the first digit. In order to avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously described embodiment are not elucidated again at a later position of the description.

[0068] FIG. 1 shows a wind turbine 1 according to embodiments of the invention. The wind turbine 1 comprises a tower 2, which is mounted on a non-depicted foundation. A nacelle 3 is arranged on top of the tower 2. The wind turbine 1 further comprises a wind rotor 5 having at least one blade 4 (in the embodiment of FIG. 1, the wind rotor comprises three blades 4, of which only two blades 4 are visible). The wind rotor 5 is rotatable around a rotational axis Y. The blades 4 extend substantially radially with respect to the rotational axis Y and along a respective longitudinal axis X.

[0069] The wind turbine 1 comprises an electric generator 11, including a stator 20 and a rotor 30. The rotor 30 is rotatable with respect to the stator 20 about the rotational axis Y. The wind rotor 5 is rotationally coupled with the electric generator 11 either directly, e.g. direct drive or by means of a rotatable main shaft 9 and/or through a gear box (not shown in FIG. 1). A schematically depicted bearing assembly 8 is provided in order to hold in place the main shaft 9 and the rotor 5. The rotatable main shaft 9 extends along the rotational axis Y.

[0070] The wind rotor 5 comprises three flanges 15 for connecting a respective blade 4 to the wind rotor 5. A pitch bearing is interposed between each blade flange 15 and the respective blade 4. A hydraulic pitch actuation circuit is associated to the pitch bearings of the blades 4 for regulating the pitch angle of each blade, i.e. the angular position of each blade about the respective blade longitudinal axis X. The hydraulic pitch actuation circuit may adjust all pitch angles on all rotor blades 4 at the same time and/or individual pitching of the rotor blades 4 may be available.

[0071] The wind turbine 1 comprises a controller (not shown) with a processor and a memory. The processor executes computing tasks based on instructions stored in the memory. According to such tasks, the wind turbine in operation generates a requested power output level. Additionally, the wind turbine in operation avoids an emergency shutdown and maintains the current hydraulic pressure above the minimum required hydraulic pressure, particularly above the offset minimum hydraulic pressure.

[0072] FIG. 2 shows a minimum requirement function 210, which may be generated by the controller for controlling the wind turbine 1. All functions are illustrated as pressure p dependent on pitch angel α functions. A dashed line illustrates a first pressure function 220 which is based on simulated blade forces which the hydraulic system of the wind turbine 1 needs to overcome to be able to pitch at least one blade 4 at a minimum speed. A dot-dashed line illustrates a second pressure function 230 which the hydraulic system of the wind turbine 1 needs to enable a reaching of a safe stop position. According to the embodiment shown in FIG. 2, the second pressure function 230 represents lower pressure values as the first pressure function 220, because in the situation of reaching of the safe stop position, a safety accumulator may help such that the needed pressure is lower. According to the present embodiment shown in FIG. 2, the minimum requirement function 210 is determined by a section-wise linear interpolation of the first pressure function 220.

[0073] The minimum requirement function 210 comprises a first section 211 being constant at a third pressure p.sub.3 at a pitch angle range extending from a first pitch angle cu to a second pitch angle α.sub.2. The first pitch angle cu is 0° and represents an operation position of the at least one blade 4. In the operation position the normal of the chord of the at least one blade 4 and the incoming wind direction enclose the pitch angle cu of 0°. The minimum requirement function 210 further comprises a second section 212 and a third section 213, wherein the second section 212 extends between the first section 211 and the third section 213. The second section 212 is determined by a linear interpolation extending from the third pressure p.sub.3 at the second pitch angle α.sub.2 to a second pressure p.sub.2 at a third pitch angle α.sub.3, wherein the second pressure p.sub.2 is lower than the third pressure p.sub.3 and the second pitch angle α.sub.2 is smaller than the third pitch angle α.sub.3 which is in the exemplary embodiment α.sub.3 equal 20°. The third section 213 is determined by a linear interpolation extending from the second pressure p.sub.2 at the third pitch angle α.sub.3 to a first pressure p.sub.1 at a fourth pitch angle α.sub.4, wherein the first pressure p.sub.1 is lower than the second pressure p.sub.2 and the third pitch angle α.sub.3 is smaller than the fourth pitch angle α.sub.4 which is in the exemplary embodiment α.sub.4=90°. At the fourth pitch angle α.sub.4 equal 90°, the at least one blade 4 is in a stop position. In the stop position at the fourth pitch angle α.sub.4 is equal to 90°, the normal of the at least one blade 4 and the incoming wind direction enclose the fourth pitch angle 4 of 90°. In other words, the at least one blade 4 is turned into the wind and the at least one blade 4 of the wind turbine 1 stops to rotate.

[0074] As may be seen in FIG. 2 at all times the minimum requirement function 210 is at least on or above the first pressure function 220 of the wind turbine 1.

[0075] FIG. 3 shows the minimum requirement function 210 as described above in connection with FIG. 2, and a hydraulic pressure function 340 of the wind turbine 1 representing the hydraulic pressure p required in the at least one accumulator dependent on the pitch angle α of the wind turbine.

[0076] The minimum requirement function 210 is determined by the above described section-wise linear interpolation as described above in connection with FIG. 2. The hydraulic pressure function 340 as illustrated in FIG. 3 illustrates the hydraulic pressure p dependent on the pitch angle α of the wind turbine 1. When a gust hits the wind turbine 1 a lot of pitch activity may be required from the controller of the wind turbine 1.

[0077] At a first system state 341 a gust hits the wind turbine. The actual pressure at the time when the gust hits the wind turbine 1 is p.sub.7 at a pitch angle α.sub.7. Due to the gust the at least one blade 4 pitches out and the hydraulic pressure drops from the pressure p.sub.7 to a pressure p.sub.5 which is below the pressure p.sub.7. At the same time due to the pitching out, the pitch angle α.sub.5 at a second system state 342 is larger than the pitch angle α.sub.7. Due to a detection of the lower pressure p.sub.5, at least one pump of the wind turbine 1 activates and starts adding hydraulic pressure into the at least one accumulator. This is illustrated in FIG. 3 in a third system state 343. During the reaction of the wind turbine 1, which takes time, the pressure p.sub.8 at the third system state 343 at the pitch angle α.sub.8 is lower than the pressure p.sub.5 at the second system state 342. At the same time the pitching out continues from the second system state 342 to the third system state 343.

[0078] When the gust has past and/or enough pressure is added to the hydraulic accumulators of the wind turbine 1, the pressure increases again from the pressure p.sub.8 at the third system state 343 to a pressure P.sub.9 at a fourth system state 344. A pitch angle α.sub.9 at the fourth system state 344 is larger than the pitch angle as at the third system state 343 due to the reaction time of the wind turbine 1. Afterwards, the pressure further increases to reach a pressure p.sub.6 at a fifth system state 345. Additionally, the at least one blade 4 of the wind turbine 1 also pitches in again. Hence, a pitch angle α.sub.6 of the at least one blade 4 is smaller than the pitch angle α.sub.9 at the fourth system state 344.

[0079] All of the hydraulic pressure values of the first system state 341, the second system state 342, the third system state 343, the fourth system state 344 and the fifth system state 345 are above the minimum requirement function 210 such that a shutdown due to too low available hydraulic pressure of the wind turbine 1 may be prevented.

[0080] FIG. 4 shows an offset minimum requirement function 410, which may be generated by the controller for controlling the wind turbine 1.

[0081] After having generated the minimum requirement function 210 by the controller as described above in connection with FIG. 2, the offset minimum requirement function 410 is determined by the predetermined positive offset 420 being constant and having a value of e.g. 10 bar. The minimum requirement function 210 may be the shutdown level at which the wind turbine shuts down. The offset minimum function may be defined as a predetermined positive offset 420 to the minimum requirement function 210.

[0082] The minimum requirement function 210 s section-wise linear and correspondingly the offset minimum requirement function 410 is section-wise linear. Additionally, the predetermined positive offset 420 is constant and therefore a distance between the minimum requirement function 210 and the offset minimum requirement function 410 is constant along the pitch angle α.

[0083] As illustrated in FIG. 4, at the first pitch angle α.sub.1, the minimum requirement function comprises a first pressure p.sub.1 and the offset minimum requirement function 410 comprises a second pressure p.sub.2 which is offset to the minimum requirement function 210 by the predetermined positive offset 420. The same is true for the second pitch angle as at which the minimum requirement function 210 comprises a third pressure p.sub.3 being lower than the first pressure p.sub.1 and the second pressure p.sub.2, and the offset minimum requirement function 410 comprises a fourth pressure p.sub.4 which is offset to the minimum requirement function 210 by the predetermined positive offset 420. The predetermined positive offset 420 at the first pitch angle α.sub.1 and the second pitch angle α.sub.2 is the same.

[0084] FIG. 5 shows the minimum requirement function 210 and the offset minimum requirement function 410 as described above in connection with FIG. 4. Additionally, a pitch adjustment speed towards a stop position 530 and a pitch adjustment speed towards an operation position 560 is depicted in FIG. 5.

[0085] The pitch adjustment speed towards the stop position 530 does not change dependent on the hydraulic pressure and is set to 100%. The pitch adjustment speed towards the operation position 560 is changed/scaled from 100% at a second pressure p.sub.2 being the offset minimum required hydraulic pressure to 0% at a first pressure p.sub.1 being the minimum required pressure in a linear way.

[0086] FIG. 6 shows the minimum requirement function 210 and the offset minimum requirement function 410 as described above in connection with FIG. 4. Additionally, a pitch adjustment speed towards a stop position 630 and the pitch adjustment speed towards an operation position 560 is depicted in FIG. 6.

[0087] The pitch adjustment speed towards the operation position 560 is changed/scaled from 100% at a second pressure p.sub.2 being the offset minimum required hydraulic pressure to 0% at a first pressure p.sub.1 being the minimum required pressure in a linear way. Additionally, a pitch adjustment speed towards the stop position 630 may be reduced to 50% of the nominal pitch adjustment speed as long as operation conditions are considered safe. Hence, the pitch adjustment speed towards the stop position 630 represents a pitching out speed and is changed/scaled from 100% at the second pressure p.sub.2 being the offset minimum required hydraulic pressure to 50% at the first pressure p.sub.1 being the minimum required pressure in a linear way. Thereby, in a case where the rotor comes close to an overspeed limit, a limitation of the pitch adjustment speed may be removed.

[0088] FIG. 7 shows the minimum requirement function 210 as described above in connection with FIG. 2, the offset minimum requirement function 410 as described above in connection with FIG. 4, and a hydraulic pressure function 740 of the wind turbine 1 representing the hydraulic pressure required in the at least one accumulator dependent on the pitch angle α of the wind turbine 1.

[0089] In a start-up case the wind turbine 1 starts at a first system state 741 being defined by a first pitch angle α.sub.1 of 86° and a first pressure p.sub.1 comprising nominal pressure. In a subsequent step, the at least one blade 4 pitches in until a second system state 742 may be reached. The second system state 742 is defined by a second pressure p.sub.2 comprising a lower pressure than the first pressure p.sub.1, and a second pitch angle α.sub.2 of e.g. 60°. At the second system state 742 the pitching stops and hydraulic pressure is added to the at least one accumulator by a at least one hydraulic pump until a third system state 743 is reached which is defined by the second pitch angle α.sub.2 and the first pressure p.sub.1. Solely if the third system state 743 is reached, the at least one blade 4 will continue to pitch in towards the operation position.

[0090] In the case of for example a broken pump or in the case of a slightly under dimensioned hydraulic system, either the at least one accumulator or the at least one hydraulic pump, the at least one hydraulic pump may not keep the pressure above the offset minimum required pressure being defined by the offset minimum requirement function 410. Therefore, a fourth system state 744 is reached defined by a fourth pressure p.sub.4 equal to the offset minimum required pressure at a fourth pitch angle α.sub.4, and the fourth pitch angle α.sub.4. In the following step, the controller controls the wind turbine 1 such that the pitch adjustment speed is slowed down such that the current hydraulic pressure stays above the minimum required hydraulic pressure defined by the minimum requirement function 210. Therefore, a fifth system state 745 is reached, which is defined by a fifth pressure p.sub.5 and a fifth pitch angle α.sub.5. The fifth pressure p.sub.5 is below the offset minimum requirement function 410 and above the minimum requirement function 210. Hence, the wind turbine 1 continued to operate and does not shutdown.

[0091] Subsequently, the pitch adjustment speed follows a maximum hydraulic pump capacity present in the wind turbine 1 and further pitches in towards the production position. This is represented by a sixth system state 746 in FIG. 7 defined by a sixth pressure p.sub.6 being higher than the fifth pressure p.sub.5 and still below the offset minimum required pressure at a sixth pitch angle α.sub.6, and the sixth pitch angle α.sub.6. At the operation position a seventh system state 747 is reached defined by a seventh pressure p.sub.7 being higher than the sixth pressure p.sub.6 as well as higher than the offset minimum requirement function 410, and a seventh pitch angle cu equal to the nominal pitch angle at the production position, e.g. 1°.

[0092] FIG. 8 shows the minimum requirement function 210 as described above in connection with FIG. 2, the offset minimum requirement function 410 as described above in connection with FIG. 4, and a hydraulic pressure function 840 of the wind turbine 1 representing the hydraulic pressure required in the at least one accumulator dependent on the pitch angle α of the wind turbine.

[0093] In the case of a broken hydraulic pump, the wind turbine 1 may produce power in a limping mode to make sure that the availability is higher than with a complete shutdown. Similarly, in the case of a sever gust, where the at least one blade 4 needs to pitch out more than is accounted for in the design of the wind turbine 1, a shutdown may be inhibited.

[0094] In a first system state 841 the wind turbine 1 operates in normal operation in the operation position with a first pressure p.sub.1 and a first pitch angle α.sub.1. Subsequently, when a sever gust hits the at least one blade 4 in normal operation or a small gust hits the at least one blade 4 in the limping mode, the at least one blade 4 pitches out and the wind turbine 1 reaches a second system state 842 defined by a second pressure p.sub.2 and a second pitch angle α.sub.2. The second pressure p.sub.2 being smaller than the offset minimum required hydraulic pressure defined by the offset minimum requirement function 410, and larger than the minimum required hydraulic pressure defined by the minimum requirement function 210. The pitch adjustment speed towards the stop position is not affected and the pressure continues to drop during a pitch out activity of the at least one blade 4. Therefore, a third system state 843 is reached defined by a third pressure p.sub.3 being smaller than the second pressure p.sub.2, smaller than the offset minimum required hydraulic pressure but still larger than the minimum required hydraulic pressure, and a third pitch angle α.sub.3 being larger than the second pitch angle α.sub.2.

[0095] Subsequently, the pitch adjustment speed towards an operation position is reduced such that the at least one hydraulic pump may be filled with hydraulic pressure again. A fourth system state 844 is reached defined by a fourth pressure p.sub.4 and a fourth pitch angle α.sub.4. The fourth pressure p.sub.4 is larger than the offset minimum required hydraulic pressure defined by the offset minimum requirement function 410, and the fourth pitch angle α.sub.4 is smaller than the third pitch angle α.sub.3 as well as larger than the second pitch angle α.sub.2. The at least one hydraulic pump continues to be filled with hydraulic pressure such that a fifth system state 845 is reached, defined by a fifth pressure p.sub.5 and a fifth pitch angle α.sub.5 being for example 1°.

[0096] Although the present invention has been disclosed in the form of preferred 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.

[0097] 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.