Wind turbine and method for controlling the wind turbine using an operating characteristic curve

Abstract

A wind turbine includes a tower, an aerodynamic rotor operable at a variable rotor speed and having a plurality of rotor blades each having an adjustable rotor blade setting angle and a generator for generating an electrical output power. An operating characteristic curve is prespecified for operating the wind turbine. The operating characteristic curve indicates a relationship between the rotor speed and the output power. A controller is provided, which sets the output power in accordance with the operating characteristic curve depending on the rotor speed. The the operating characteristic curve has a starting rotation speed to which the rotor speed increases as soon as the wind turbine starts when a sufficient wind speed is reached. The starting rotation speed is defined depending on a tower natural frequency of the wind turbine and/or depending on a detected turbulence measure of the prevailing wind.

Claims

1. A wind turbine, comprising: a tower; an aerodynamic rotor operable at a variable rotor speed and having a plurality of rotor blades, each blade having an adjustable rotor blade setting angle; a generator configured to generate an electrical output power during a power supplying operation, wherein an operating characteristic curve is prespecified for operating the wind turbine and the operating characteristic curve defines a relationship between the rotor speed and the output power; and a controller configured to set the output power to a value of the operating characteristic curve corresponding to a value of the rotor speed, wherein: the operating characteristic curve has a starting rotation speed to which the rotor speed increases in response to both the wind turbine starting and a sufficient wind speed being reached, the starting rotation speed corresponding to a rotor speed at which the generator is controlled to start generating the output power, and the starting rotation speed is determined, prior to the power supplying operation, depending on a tower natural frequency of the wind turbine.

2. The wind turbine as claimed in claim 1, wherein: the operating characteristic curve specifies a starting output power value associated with the starting rotation speed, and the controller is configured to set the output power to the starting output power value in response to the wind turbine starting, the starting output power value being generated by the generator until the sufficient wind speed is exceeded.

3. The wind turbine as claimed in claim 2, wherein when either a wind speed increases to the sufficient wind speed or a rotor torque increases to a starting torque, the rotor speed increases to the starting rotation speed, the controller sets the starting output power value and the generator generates the starting output power value.

4. The wind turbine as claimed in claim 1, wherein the operating characteristic curve is selected from a plurality of predetermined operating characteristic curves.

5. The wind turbine as claimed in claim 1, wherein a starting rotor blade setting angle is associated with the starting rotation speed, and wherein the starting rotation speed is positively correlated with the starting rotor blade setting angle such that the starting rotation speed increases as the starting rotor blade setting angle increases and the starting rotation speed decreases as the starting rotor blade setting angle decreases.

6. The wind turbine as claimed in claim 1, wherein: the controller is configured to select a tip-speed ratio for the starting rotation speed depending on the starting rotation speed or depending on a starting rotor blade setting angle, the controller being configured to select the tip-speed ratio for the starting rotation speed such that: the starting rotation speed is positively correlated with the tip-speed ratio such that the tip-speed ratio increases as the starting rotation speed increases and the tip-speed ratio decreases as the starting rotation speed decreases, and the starting rotor blade setting angle is positively correlated with the tip-speed ratio such that the tip-speed ratio increases as the starting rotor blade setting angle increases and the tip-speed ratio decreases as the starting rotor blade setting angle decreases.

7. The wind turbine as claimed in claim 1, wherein the starting rotation speed is also determined depending on a turbulence intensity of winds acting on the wind turbine over a period of time, the turbulence intensity being determined based on respective wind speeds of the winds.

8. The wind turbine as claimed in claim 7, wherein: the turbulence intensity is positively correlated with a variation in the wind speeds during the period of time such that the turbulence intensity increases as the variation increases and the turbulence intensity decreases as the variation decreases, and the turbulence intensity is positively correlated with the starting rotation speed such that the starting rotation speed increases as the turbulence intensity increases and the starting rotation speed decreases as the turbulence intensity decreases.

9. The wind turbine as claimed in claim 7, wherein the starting rotation speed is selected such that the starting rotation speed is greater than a rotor speed which excites the tower natural frequency.

10. The wind turbine as claimed in claim 9, wherein: the starting rotation speed is selected such that a blade pass frequency is greater than the tower natural frequency, the blade pass frequency being a frequency at which the plurality of rotor blades pass by a specified point during rotation of the plurality of rotor blades.

11. The wind turbine as claimed in claim 10, wherein the blade pass frequency is between 5% and 25% above the tower natural frequency.

12. The wind turbine as claimed in claim 10, wherein the blade pass frequency is at least 5% above the tower natural frequency.

13. The wind turbine as claimed in claim 7, wherein: the rotor speed is adjusted depending on the turbulence intensity to set the starting rotation speed.

14. The wind turbine as claimed in claim 13, wherein the rotor rotates in a coasting mode in which the generator does not generate the output power.

15. The wind turbine as claimed in claim 7, wherein the wind speeds of the winds acting on the wind turbine over the period of time are determined indirectly from an operating behavior of the wind turbine, the operating behavior including the rotor speed, a rotor torque, the output power or the rotor blade setting angles of the plurality of blades of the wind turbine.

16. A method for controlling a wind turbine, wherein the wind turbine includes: a tower, an aerodynamic rotor operable at a rotor speed that is variable and having a plurality of rotor blades, each blade having an adjustable rotor blade setting angle, and a generator configured to generate an output power, and the method comprises: during a power supplying operation, operating the wind turbine using a prespecified operating characteristic curve which defines a relationship between the rotor speed and the output power; setting the output power to a value of the operating characteristic curve corresponding to a value of the rotor speed, wherein the operating characteristic curve has a starting rotation speed, the starting rotation speed corresponding to a rotor speed at which the generator is controlled to start generating the output power; determining, prior to the power supplying operation, the starting rotation speed depending on a tower natural frequency of the wind turbine; and in response to both the wind turbine starting, by allowing rotation of the rotor, and a sufficient wind speed being reached, increasing the rotor speed to the starting rotation speed.

17. The method as claimed in claim 16, wherein a starting output power value is generated by the generator until the sufficient wind speed is exceeded.

18. The method as claimed in claim 16, wherein a starting rotor blade setting angle is associated with the starting rotation speed and the starting rotation speed is positively correlated with the starting rotor blade setting angle such that the starting rotation speed increases as the starting rotor blade setting angle increases and the starting rotation speed decreases as the starting rotor blade setting angle decreases.

19. The method as claimed in claim 16, wherein the starting rotation speed is determined also depending on a turbulence intensity of winds acting on the wind turbine over a period of time, the turbulence intensity being determined based on respective wind speeds of the winds.

20. The method as claimed in claim 19, wherein: the turbulence intensity is positively correlated with the starting rotation speed such that the starting rotation speed increases as the turbulence intensity increases and the starting rotation speed decreases as the turbulence intensity decreases.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

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

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

(3) FIG. 2 shows various operating characteristic curves with different starting rotation speeds.

(4) FIG. 3 shows various wind speed-dependent rotation speed profiles and associated blade setting angles.

(5) FIG. 4 shows a schematic flow chart of a wind turbine controller or a corresponding method.

DETAILED DESCRIPTION

(6) FIG. 1 shows a wind turbine 100 comprising 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 set in rotary motion by the wind during operation and in this way drives a generator in the nacelle 104.

(7) FIG. 2 shows an operating characteristic curve 200 which shows a power P as a function of the rotation speed n. The power P is standardized to nominal power P.sub.N and the rotation speed n is standardized to its nominal rotation speed n.sub.N in the graph.

(8) In addition, a critical rotation speed n.sub.K is marked in the graph of FIG. 2. This critical rotation speed n.sub.K is a rotation speed which would excite a tower natural frequency. For example, this critical rotation speed n.sub.K can be that rotation speed at which a blade pass frequency is established for a wind turbine with three rotor blades, as is shown in FIG. 1, in accordance with the natural frequency of the tower of the wind turbine.

(9) In FIG. 2, the operating characteristic curve 200 has three variations which accordingly lead to three different characteristic curve segments 201 to 203. In this case, the first characteristic curve segment 201 shows a variation in which the critical rotation speed n.sub.K is not avoided. Therefore, in this first characteristic curve segment 201, the wind turbine starts at the minimum rotation speed n.sub.m which constitutes a starting rotation speed in this respect. It can be seen that, according to this operating characteristic curve with the first characteristic curve segment 201, the rotation speed has this value of the minimum rotation speed n.sub.m during starting, wherein the power initially increases to the minimum power P.sub.m at the start, that is to say when the wind is still weak. Said minimum power is the power which has to be generated at least expediently by the wind turbine or by its generator so that starting of the wind turbine is actually expedient.

(10) As the wind speed rises, the rotation speed and therefore also the power then also increase, wherein the critical speed n.sub.K is then achieved in the interim. Excitation of the natural frequency of the tower of the wind turbine can then occur, and this excitation can lead to high loading of the wind turbine.

(11) In order to avoid this, it is proposed to select a starting rotation speed n.sub.ST which lies above the critical rotation speed n.sub.K. Owing to this solution, the critical rotation speed n.sub.K therefore does not need to be passed through, as proposed in some other methods, but rather starting is just implemented at a higher rotation speed.

(12) Two options for this are illustrated in FIG. 2. According to the second characteristic curve segment 202, a solution is proposed here in which the starting rotation speed n.sub.ST is only slightly higher than the critical rotation speed n.sub.K.

(13) However, the wind turbine also starts substantially at the minimum power P.sub.m according to this second characteristic curve segment 202, which is likewise part of the operating characteristic curve 200. To this end, substantially only a different starting rotation speed which is, specifically, higher than the minimum rotation speed n.sub.m is selected. If the wind speed then increases, the rotation speed also increases there and in the process the operating point, which is determined by the respective power value and rotation speed value here, moves to the main segment 204 of the operating characteristic curve 200, in which main segment the three characteristic curve segments 201 to 203 merge.

(14) In addition, it is now proposed that it is also further possible to take into consideration the level of the turbulence of the wind. To this end, a turbulence intensity is calculated in particular and if said turbulence intensity is high, it is proposed to select a yet further distance of the starting rotation speed n.sub.ST from the critical rotation speed n.sub.K than is the case in the second characteristic curve segment 202. Accordingly, the third characteristic curve segment 203 is proposed given a high turbulence intensity. The wind turbine initially starts at a power value approximately at the level of the minimum power P.sub.m in said third characteristic curve segment too. If the wind speed increases further, the operating point is adjusted to the main segment 204 of the operating characteristic curve 200 here too. Therefore, the third characteristic curve segment 203 creates a greater distance from the critical rotation speed and as a result can prevent additional loading due to a high turbulence intensity.

(15) FIG. 3 exhibits a combined graph, specifically the illustration of a rotation speed profile n as a function of a wind speed V.sub.W. The lower region of this graph shows associated blade setting angles α.

(16) FIG. 3 therefore shows, in the upper section, a rotation speed characteristic curve 300 which is basically associated with the operating characteristic curve 200 of FIG. 2, wherein it should of course be noted that the illustrations are schematic. Accordingly, this rotation speed characteristic curve 300 also has a first to third characteristic curve segment 301 to 303 which basically belong to the first to third characteristic curve segment 201 to 203 of FIG. 2 or can be associated with said characteristic curve segments in the same order. The rotation speed characteristic curve 300 also has a main segment 304 in which the rotation speed characteristic curve 300 for all three variants is then the same.

(17) Moreover, the wind speed V.sub.W is standardized to the nominal wind speed V.sub.N and the rotation speed n is standardized to its nominal rotation speed n.sub.N here too. The blade setting angles illustrated in the lower section are indicated, by way of example, by angular degrees which can also have other values.

(18) Therefore, the first characteristic curve segment 301 starts at a low wind speed V.sub.m and is then raised to the minimum rotation speed n.sub.m or the turbine controller allows the wind to speed up the rotor to this rotation speed. If the wind speed then increases further, the rotation speed also increases further, until it has reached the main segment 304 of the rotation speed characteristic curve 300. In this case, said rotation speed has to pass through the critical rotation speed n.sub.K, which can lead to undesired loadings. A first characteristic curve segment 311 of a blade setting angle profile 310 is associated with this first characteristic curve segment 301 of the rotation speed characteristic curve. This shows that the blade setting angle which is associated with the first characteristic curve segment 301 of the rotation speed characteristic curve 300 remains constant over the entire wind speed under consideration. This is marked by way of example there by a rotor blade setting angle of 4 degrees.

(19) According to a second characteristic curve segment 302 of the rotation speed characteristic curve 300, it is proposed to immediately increase the rotation speed to a starting rotation speed n.sub.ST when the minimum wind speed V.sub.m is reached. This starting rotation speed n.sub.ST of the second characteristic curve segment 302 lies above the critical rotation speed n.sub.K. Although the second characteristic curve segment 302 also intersects the critical rotation speed n.sub.K, it does not have a stationary operating point at this critical rotation speed n.sub.K. In this respect, said second characteristic curve segment differs from the first characteristic curve segment 301 which has a critical operating point 321 which forms a stationary operating point. A tower natural frequency is excited at this stationary operating point, specifically the critical operating point 321, this leading to undesired loading.

(20) A blade setting angle according to the second characteristic curve segment 312 of the blade setting angle profile 310 is associated with the second characteristic curve segment 302, which blade setting angle initially, that is to say at low wind speeds V.sub.W, has a greater value than the main segment 314 of the blade setting angle profile 310. This angle of the second characteristic curve segment 312 is initially indicated by 6 degrees by way of example here. As the wind speed increases, this blade setting angle initially remains constant but then drops to the value of the main segment 314. At this point, the second characteristic curve segment 302 of the rotation speed characteristic curve 300 then also reaches the main segment 304 of the rotation speed characteristic curve 300.

(21) The situation is also very similar for the third characteristic curve segment 303 of the rotation speed characteristic curve 300 which reaches an even higher starting rotation speed n.sub.ST when the minimum wind speed V.sub.m is reached, and therefore assumes an even greater distance from the critical rotation speed n.sub.K likewise right at the beginning. The third characteristic curve segment 303 also intersects the critical rotation speed n.sub.K, but does not have a stationary operating point there. The third characteristic curve segment 303 of the rotation speed characteristic curve 300 then also approaches the main segment 304 of the rotation speed characteristic curve 300 as the wind speed V.sub.W increases. When it reaches this main segment 304, it then also has the same rotor blade setting angle as the main segment 314 of the blade setting angle profile 310. However, a third characteristic curve segment 313 of the blade setting angle profile 310 can be seen in front of it, said third characteristic curve segment being associated with the third characteristic curve segment 303 of the rotation speed characteristic curve 300 and exhibiting an even greater blade setting angle there, which blade setting angle is indicated by the value of approximately 8 degrees by way of example.

(22) FIG. 3 is intended to particularly illustrate that a starting rotation speed n.sub.ST which is selected to be considerably higher, as is also shown in FIG. 2, does not mean that the wind turbine starts later depending on the wind speed, but rather only that it starts in a different way. Although slight differences in the minimum wind speed V.sub.m, at which these different characteristic curves start, are taken into consideration, these differences are small and therefore only a minimum wind speed V.sub.m is marked in FIG. 3 too.

(23) FIG. 4 now shows a flow diagram according to which this flow chart 400 starts with the identification block 402. In the identification block 402, the resonant frequency f.sub.R is initially detected or identified. This can be done by way of this resonant frequency being ascertained on the basis of knowledge about the wind turbine. This can also mean that it is already prespecified at the development end and is implemented in a process computer. In this respect, the flow chart 400 is also understood to be a controller in which the flow chart outlined is implemented. This resonant frequency f.sub.R can also be stored in this controller by the manufacturer and as a result form an input variable in this flow chart 400.

(24) The critical rotation speed n.sub.K is calculated from this resonant frequency or natural frequency of the tower of the wind turbine in the calculation block 404 in any case. As a calculation for this, consideration is given to it being assumed that the critical rotation speed n.sub.K corresponds to the rotation speed which has a blade pass frequency which corresponds to the natural frequency or resonant frequency f.sub.R.

(25) Based on this critical rotation speed n.sub.K, a starting rotation speed n.sub.ST is then calculated in the simplified starting rotation speed block 406. This can be done, for example, by way of said starting rotation speed being set to a value of 5% above the critical rotation speed n.sub.K. It is preferably set to a value in the range of from 5 to 25% above the critical rotation speed n.sub.K.

(26) It is then proposed to additionally detect a turbulence measure. For this purpose, the turbulence intensity block 408 ascertains a turbulence intensity. This can be done, for example, based on wind speed measurements. Therefore, the turbulence intensity block 408 is also characterized as an input block. From these two values, specifically the simplified starting rotation speed n.sub.ST and the turbulence intensity T.sub.i, the starting rotation speed n.sub.ST is then determined in the complete starting rotation speed block 410.

(27) The starting rotation speed n.sub.ST determined in this way is then input into the starting operating point block 412. In the starting operating point block 412, the starting power P.sub.ST and the starting rotor blade setting angle α.sub.ST are determined from the starting rotation speed n.sub.ST. These three values, that is to say the starting rotation speed n.sub.ST, the starting power P.sub.ST and the starting rotor blade setting angle α.sub.ST, then define the operating point to be set. This operating point, that is to say the three values mentioned, is given in the starting block 414. However, starting is implemented only when there is a sufficiently high wind speed V.sub.W. This is determined by the wind block 416 and input into the starting block 414. As an alternative, it is proposed that, instead of detecting the wind speed, a torque is used as the basis and starting is then implemented only when, owing to the wind, there is a predetermined starting torque. For this alternative, the wind block 416 can then be in the form of a starting torque block.

(28) In principle, this flow chart 400 is a schematic illustration and all blocks described can also be combined or partially combined, particularly in corresponding software in a process computer. However, it should be noted in particular that the turbulence intensity block 408 and the wind block 416 can share the same data in particular. For example, the wind block 416 can receive the wind speed data, for example, by a corresponding sensor and pass said data firstly into the starting block 414 but secondly also transfer said data to the turbulence intensity block 408 for evaluation purposes.

(29) In any case, according to the starting block 414, the wind turbine is then started when the wind speed, which the wind block 416 has transferred, is sufficiently high. As an alternative, a torque can also be taken into consideration here and can be compared with a predetermined starting torque. The wind turbine is then started and this means, in particular, that the rotor blade setting angle α is then initially set to the starting rotor blade setting angle α.sub.ST. In addition, the rotor speed n is set to the starting rotation speed n.sub.ST and the output power P can also be set to the starting output power P.sub.ST. These are particular starting conditions which have been determined in the starting operating point block 412.

(30) If the wind speed is further increased, the values can then be adapted however. This can be done, in particular, as is prespecified by corresponding characteristic curves, specifically particularly by a rotation speed characteristic curve as shown in FIG. 2 and a blade setting angle profile as shown in the lower region of FIG. 3. The rotation speed characteristic curve 300 of FIG. 3 serves substantially for illustration purposes, but does not form a characteristic curve which controls the wind turbine. However, the starting wind speed, which is recorded there as the minimum wind speed V.sub.m, can preferably be taken into account in the starting block 414.

LIST OF REFERENCE SIGNS

(31) Wind turbine 100 Tower 102 Nacelle 104 Rotor 106 Rotor blades 108 Spinner 110 Power P/Output power P Nominal power P.sub.N Minimum power P.sub.m Starting power P.sub.ST/Starting output power P.sub.ST Rotation speed n/Rotation speed profile n/Rotor speed n Starting rotation speed n.sub.ST Nominal rotation speed n.sub.N Critical rotation speed n.sub.K Minimum rotation speed n.sub.m Operating characteristic curve 200 First characteristic curve segment 201 Second characteristic curve segment 202 Third characteristic curve segment 203 Main segment 204 Wind speed V.sub.W Nominal wind speed V.sub.N Low wind speed/Minimum wind speed V.sub.m Blade setting angle α Starting rotor blade setting angle α.sub.ST Rotation speed characteristic curve 300 First characteristic curve segment 301 Second characteristic curve segment 302 Third characteristic curve segment 303 Main segment 304 Blade setting angle profile 310 First characteristic curve segment 311 Second characteristic curve segment 312 Third characteristic curve segment 313 Main segment 314 Critical operating point 321 Flow chart 400 Identification block 402 Resonant frequency f.sub.R Calculation block 404 Simplified starting rotation speed block 406 Simplified starting rotation speed n.sub.ST Turbulence intensity block 408 Turbulence intensity T.sub.i Complete starting rotation speed block 410 Starting operating point block 412 Starting block 414 Wind block 416