Novel rotor effective wind speed estimation method for light detection and ranging application

Abstract

In recent researches, the “Cyclops” effect of the light detection and ranging (LiDAR) system has been revealed, which presents the shortcoming of LiDAR measurement. The “Cyclops” effect means that the LiDAR system can only measure wind speed at one point in space at a certain moment. Thus, for the wind turbine control concern, considering the wind information at the rotor plane with time-stamps can be more precise. Taylor's frozen hypothesis is commonly used in the application of LiDAR for the rotor effective wind speed estimation. It assumes that the wind moves with the speed unchanged when getting close to the turbine. Thus, the time of the wind transmission can be easily calculated. In fact, the wind speed attenuates along the process from the LiDAR measured point to the rotor plane because of the induction zone. Without considering the attenuation effect, the wind turbine is controlled directly by LiDAR measured data with constant time delay, which weakens the effectiveness of LiDAR. In this paper, a novel LiDAR data pre-processing method is demonstrated for rotor effective wind speed estimation. In this method, the Medici induction zone model is further refined with initial wind speed and different measured distances for accurate estimation. Furthermore, it makes online variable time delay of LiDAR data computation possible with the solution of the separated differential equation. Finally, the novel method is fully verified through field test results. The results show that the initial wind speed affected the attenuation factor within 1.4 times rotor radius and the error between the experimental value and the theoretical value is within 0.1m/s.