Wavelet based feed forward wind gust control of wind turbines

Interest in using LIDARs for control of wind turbines have in the last couple of years dramatically increased. Purposes have been to improve control of fatigue and extreme load cases. It is clearly beneficial if the wind field can be known in advance before the wind field meets the wind turbine rotor. However, most works have assumed a frozen turbulence; basically meaning that the wind field would change from the measurement at the LIDAR to it hits the wind turbine rotor. Some work have been published on using extracted features from the LIDAR measurement, which describes e.g. the general trends of the mean wind speed, which can be used for control of the wind turbine in case of a wind gust. The point is that if a wind gust is measured in front of the wind turbine is quite certain that it will hit the wind turbine in short given time, however, the amplitude and shape of the wind gust might changes a bit especially if the spatial distribution of the wind field considered as well. The features are selected to describing the general trends of the wind gust, which can be expected to be seen at the wind turbine as well. A wind gust is something which has a compact support both in time and frequency; it is therefore very relevant to use a joint time and frequency basis to extract these relevant features. Wavelet basis is such a joint time and frequency basis, which is often used to extract and support features in signals with properties similar to a mean wind speed measurement with wind gusts. An additional advantage of using a wavelet basis for the feature extraction is that the basis vectors can be scale in length according to the time length of the wind gust. In this work a scheme which extracts features using a wavelet basis from a mean wind speed measurement from a LIDAR in front of a wind turbine is proposed, the extracted features are used in a feed forward control scheme which provides and add on pitch control signal to the standard power and speed controller. The proposed scheme is applied the to the 5MW NREL reference turbine using a FAST implementation of the turbine, for the simulations. These simulations show the potential of the proposed scheme.