Un-freezing the turbulence: application to LiDAR-assisted wind turbine control

Recent developments in LiDAR technology have led to much interest in the possibility of improving turbine control by using a turbine-mounted LiDAR, to provide advance information about the approaching wind field. This could significantly reduce turbine loads, bringing improved cost-effectiveness, especially for large turbines. There have also been claims of direct increases in energy capture as a result of using such preview information. This study reports on an independent study employing detailed analytical methods to evaluate the likely benefits of LiDAR-assisted control and advise LiDAR manufacturers about the characteristics of their systems, which are most likely to be useful for this application. Accurate simulation models are vital for assessing the performance of LiDARs and controllers which use them. Current models use Taylor's frozen turbulence hypothesis, but this is not strictly valid when LiDAR is used to measure upstream wind speeds, as the measured wind cannot be assumed to convect unchanged to the turbine. A method for avoiding the frozen turbulence assumption is proposed, and simulation results are presented to illustrate the effect on fatigue load reductions which LiDAR-assisted control might achieve. A detailed assessment of possible LiDAR benefits is made using the UPWIND generic 5 MW turbine as an example.