CONTROL METHOD FOR A WIND TURBINE

Abstract

A control system for yawing a wind turbine rotor relative to the wind and for changing the pitch of rotor blades. A wind direction parameter is measured by a wind direction sensor. The wind direction is calibrated as a function of a predetermined offset parameter, and then adjusted as a function of a wind direction compensation parameter. The adjusted relative wind direction is then used in the determining of a control parameter of the wind turbine. The parameters for the calibration and adjustment of the relative wind direction are obtained from a set of data comprising the wind direction relative to the wind turbine over time and as measured by the wind direction sensor on the wind turbine and as measured by a second wind direction sensor.

Claims

1. A method of controlling a wind turbine, the wind turbine comprising a wind direction sensor, a number of pitch-adjustable rotor blades, a yawing system, and a control system for yawing the wind turbine rotor relative to the wind and for changing the pitch of the rotor blades, the method comprising: measuring a wind direction parameter by the wind direction sensor, wherein the wind direction parameter is indicative of the wind direction relative to the wind turbine; calibrating the measured relative wind direction as a function of a predetermined offset parameter; adjusting the calibrated relative wind direction as a function of a wind direction compensation parameter, wherein the wind direction compensation parameter depends on the calibrated relative wind direction; determining a control parameter of the wind turbine as a function of the adjusted relative wind direction; and controlling the wind turbine according to the control parameter.

2. A method of controlling according to claim 1 further comprising obtaining a set of data comprising the wind direction relative to the wind turbine over time and as measured by the wind direction sensor on the wind turbine and as measured by a second wind direction sensor.

3. A method of controlling according to claim 2, wherein the second wind direction sensor is positioned on a nearby METmast and/or comprises a LIDAR sensor.

4. A method of controlling according to claim 2, wherein the predetermined offset parameter is determined as a mean error of the wind direction sensor measurements compared to the measurements by the second wind direction sensor.

5. A method of controlling according to claim 2, comprising pre-setting a number of intervals of wind direction as measured by the first and/or second wind direction sensor, and for each wind direction interval determining a wind direction compensation parameter for that wind direction interval and based on the sub-set of data for that wind direction interval and from the difference between the first wind direction sensor measurements and the second wind direction sensor measurements in the sub-set of data.

6. A method of controlling according to claim 2, comprising pre-setting a number of intervals of wind direction as measured by the first and/or second wind direction sensor, and for each wind direction interval determining a wind direction compensation parameter for that wind direction interval and based on the sub-set of data for that wind direction interval, by determining a first distribution function of the first wind direction sensor measurements in the sub-set of data, determining a second distribution function of the second wind direction sensor measurements in the sub-set of data, and comparing the first and second distribution functions.

7. A method of controlling according to claim 1, wherein the wind direction compensation parameter is determined as an offset value and/or a gain factor.

8. A method of controlling according to claim 2, wherein the set of data further comprises a measurement and/or an estimate of a wind speed at the time of measurement.

9. A method of controlling according to claim 2, wherein the predetermined offset parameter and/or the wind direction compensation parameter depend on the wind speed.

10. A method of controlling according to claim 8, further comprising pre-setting a number of intervals of wind speed, and determining an offset parameter and/or a wind direction compensation parameter for each wind speed interval based on the obtained data for that wind speed interval.

11. A method of controlling according to claim 10 further comprising measuring a wind speed and adjusting the relative wind direction as a function of the wind direction compensation parameter determined for the wind speed interval comprising the wind speed at the time of adjusting.

12. A method of controlling according to claim 10 further comprising measuring a wind speed and adjusting the relative wind direction by using an interpolation between the wind direction compensation parameters of the different wind speed intervals.

13. A method of controlling according to claim 1, where the control parameter comprises a pitch parameter of one or more of the rotor blades and the controlling of the wind turbine comprises pitching one or more of the blades according to the pitch parameter.

14. A method of controlling according to claim 1, wherein the control parameter comprises a yaw angle for the wind turbine and the controlling of the wind turbine comprises yawing the wind turbine according to the yawing parameter.

15. A control system for a wind turbine, comprising: an input/out (I/O) interface configured to communicate with the wind turbine; a memory containing instructions; and a processor communicatively coupled to the I/O interface and the memory, and configured to execute the instructions to perform an operation comprising: receiving a wind direction parameter as measured by a wind direction sensor, wherein the wind direction parameter is indicative of the wind direction relative to the wind turbine; calibrating the measured relative wind direction as a function of a predetermined offset parameter; adjusting the calibrated relative wind direction as a function of a wind direction compensation parameter, wherein the wind direction compensation parameter depends on the calibrated relative wind direction; determining a control parameter of the wind turbine as a function of the adjusted wind parameter; and controlling the wind turbine according to the control parameter.

16. A wind turbine, comprising: a wind sensor, a yawing system, and a control system configured to yaw the wind turbine rotor relative to the wind by performing an operation comprising: receiving a wind direction parameter as measured by a wind direction sensor, wherein the wind direction parameter is indicative of the wind direction relative to the wind turbine; calibrating the measured relative wind direction as a function of a predetermined offset parameter; adjusting the calibrated relative wind direction as a function of a wind direction compensation parameter, wherein the wind direction compensation parameter depends on the calibrated relative wind direction; determining a control parameter of the wind turbine as a function of the adjusted wind parameter; and controlling the wind turbine according to the control parameter.

17. The control system of claim 15 wherein the operation further comprises obtaining a set of data comprising the wind direction relative to the wind turbine over time and as measured by the wind direction sensor on the wind turbine and as measured by a second wind direction sensor.

18. The control system of claim 17, wherein the second wind direction sensor is positioned on a nearby METmast and/or comprises a LIDAR sensor.

19. The control system of claim 17, wherein the predetermined offset parameter is determined as a mean error of the wind direction sensor measurements compared to the measurements by the second wind direction sensor.

20. The wind turbine of claim 16, wherein the operation further comprises obtaining a set of data comprising the wind direction relative to the wind turbine over time and as measured by the wind direction sensor on the wind turbine and as measured by a second wind direction sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the following different embodiments of the invention will be described with reference to the drawings, wherein:

[0058] FIG. 1 illustrates the change in wind direction when the free flow passes through a wind turbine rotor,

[0059] FIG. 2 is a flow chart illustrating an embodiment of the invention,

[0060] FIGS. 3 and 4 illustrate the calibration and adjustment of the measured wind direction according to embodiments of the invention,

[0061] FIGS. 5 and 6 show examples of wind direction compensation parameters for two different wind speed intervals and according to embodiments of the invention, and

[0062] FIG. 7 show examples of the calibrated measured relative wind direction versus relative wind direction measured from a nearby MET mast and for different types of wind turbines.

DETAILED DESCRIPTION OF THE DRAWINGS

[0063] FIG. 1 illustrates the change in wind direction when the free flow 100 passes through a wind turbine rotor 101. If the rotor 101 is turned directly in to the wind as illustrated by the solid black line 103, a wind direction sensor 104 positioned on the nacelle 105 behind the rotor 101 when calibrated will measure a wind direction of 0 degrees. However, if the wind is not directly upwind the wind flow 100 is affected by the rotor 101 and is affected differently depending on the direction of the incoming wind. Therefore, the wind sensor 104 may detect the wind direction inaccurately. The figure illustrates how an incoming wind at approximately 45 degrees, 110, may be measured as being only 30 degrees, 111, even though the wind sensor has been calibrated.

[0064] FIG. 2 shows a flow chart illustrating the method steps performed in a control system, 200, of a wind turbine according to the invention. The control method comprises measuring a direction of the wind relative to the wind turbine by means of a wind direction sensor, 201. Then the relative wind direction as measured by the wind direction sensor is first calibrated by a predetermined offset parameter as conventionally done, 202. Hereby, the wind direction sensor is calibrated so as to yield a calibrated relative wind direction of 0 degrees when the rotor is turned directly upwind.

[0065] However, it has been observed that the calibrated wind sensor shows an error in its relative wind direction measurements when the wind turbine is not pointing directly upwind. In many cases the wind sensors have been found to yield relative wind directions smaller than the actual relative wind direction. In such cases, the inaccuracy of the wind sensor reported here may not be noticed as this could result in the wind turbine being yawed less than optimal and the wind turbine needing more yawing steps to be turned into the wind. It can however also result in, that a bigger yaw error is required before starting yawing upwind, and even worse that an extreme yaw error event may not be detected. For instance if the wind is suddenly changing 30 degrees some pitching of the blades is needed to minimize the loads. But if only 20 degrees are measured, the load reduction activities would not be initiated on the event.

[0066] In some case and for some rotor types, the rotor has been seen to affect the wind flow in such a way that the wind sensors yield relative wind directions larger than the actual relative wind direction. This may however be critical to the controlling of the wind turbine and lead to critical loads and wear especially on the yawing system, as the control system may then tend to yaw the rotor too much and causing the rotor to be yawed back and forth without obtaining the desired yaw direction of the rotor pointing directly into the wind.

[0067] This inaccuracy of the wind sensor measurements is removed by the method according to the invention by adjusting the already calibrated relative wind direction by a wind direction compensation parameter as illustrated in step 203 in FIG. 2. The wind direction compensation parameter depends on the calibrated relative wind direction. Hereby is obtained a calibrated and adjusted relative wind direction, which is then used in the control of the wind turbine.

[0068] The wind direction compensation parameter is determined from a data set of measurements of the relative wind direction as measured by a wind sensor on a wind turbine and by a wind sensor preferably on a nearby MET mast. The different curves 700 in FIG. 7 show such data for a number of different wind turbines. Here, the relative wind direction as measured on a second wind sensor on a nearby MET mast, 701 is plotted versus the relative wind direction as measured and calibrated from the first wind sensor on the wind turbine, 702. Due to the initial calibration by the offset parameter, the first wind sensor yields a relative wind direction of 0 degrees in accordance with the 0 degrees also measured by the second wind sensor on he MET mast (i.e. all the curves 700 go through the point of (0,0)). All wind sensors of the wind turbine as shown in FIG. 7 generally yield too small wind directions. However, this is not always the case and as mentioned previously, some wind turbine sensors have been seen to detect larger wind directions than the actual wind directions.

[0069] FIGS. 3 and 4 illustrate the calibration and adjustment of the raw measured wind direction data 300 according to two different embodiments of the invention and in more detail. A wind speed V, 301 is measured and/or estimated and an offset parameter 303 for that wind speed is obtained, 302. The offset parameter may be given as a pre-defined look-up table or set of offset parameters 303, preferably expressing the offset parameter as a function of the wind speed V, 301. So, based on the wind speed determination 301, the measured relative wind direction 300 is then calibrated 304 by the addition of the offset parameter 303 corresponding to that wind speed. Then the calibrated relative wind direction is adjusted 305 as a function of a wind direction compensation parameter 306 to yield a calibrated and adjusted wind direction 316 which is then used in the controller, 307. The wind direction compensation parameter 306 itself depends on the calibrated wind direction 304. The wind direction compensation parameter may further and preferably depend on the wind speed V, 301.

[0070] In the method of FIG. 3, the adjustment of the calibrated wind direction by means of the wind direction compensation parameter is performed by adding the wind direction compensation parameter as an offset value. In the method of FIG. 4, the wind direction compensation parameter is given as a gain factor, 400.

[0071] In FIGS. 5 and 6 are shown examples of wind direction compensation parameters 306 for two different wind speed intervals. The wind direction compensation parameter 306 of the wind speed interval or range as shown in FIG. 5 is seen to be given approximately by a piecewise linear function of the measured (and calibrated) relative wind direction, 304. Although the general shapes of the sets of wind direction compensation parameters 306 for the two different wind speeds in FIGS. 5 and 6, respectively, appear to have some similarities, the wind direction parameter function for wind speeds in the wind speed interval of FIG. 5 is seen to show more extreme values than of FIG. 6. In other words, the wind sensor measurements when the wind speed is in the wind speed interval of FIG. 5 are more off and need to be adjusted by larger parameters than when the wind speed is in the wind speed interval of FIG. 6.

[0072] While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.