Review of LIDAR-assisted control for floating offshore wind

Alan Whooley, Vice President, Wood
Light detection and ranging (LIDAR) technology has shown capability for effectively capturing the wind profile, particularly in terms of wind shear, veer and gust tracking. Floating LIDAR is now commonly used when performing resource assessments of potential offshore wind farm sites. The prospect of utilising nacelle-mounted LIDAR for assisting the control strategies of wind turbines has recently been proposed and partially explored. LIDAR is able to provide knowledge of the incoming wind so that the turbine can be prepared for incoming wind conditions in advance, using Feed-Forward torque, pitch, or yaw control. This methodology has demonstrated potential for improved disturbance rejection and power capture, whilst reducing the loadings and pitch rate. However, while studies have shown promising results, there has been limited uptake of LIDAR-assisted control in industrial projects. LIDAR-assisted control can aid in improving the turbine performance across its full operating range. This includes within its region 2 (above cut-in and below rated wind speed) where torque control is utilised, region 2.5 (where the rotor speed reaches its rated value before the generator torque reaches its rated value), and region 3 (above rated speed but below cut out speed), where pitch control is employed. Various control philosophies have been studied to investigate their potential for improving the turbine performance. These philosophies include, but are not limited to: Gain Scheduling, Model Predictive Control (MPC), H∞ and Filtered-X Recursive Least Squares (FX-RLS), Disturbance Tracking Control (DTC), and Optimally Tracking Rotor (OTR). This paper will provide an overview of these methodologies as well as provide a review of how they have been employed for LIDAR-assisted turbine control strategies. The primary focus of this paper is to review work and industry efforts on LIDAR-assisted control of floating offshore wind turbines. Previous studies performed on floating turbines will be reviewed, with detail provided of the key differences between fixed and floating offshore turbine behaviour. To provide context, the paper will also review the computational and practical studies that have been performed for fixed turbines and the journey and development that the field has undertaken since its conceptualisation. Finally, this paper will propose recommendations for future work on the topic, offering suggestions for how the research can better reflect the current industry landscape. For example, previous computational studies have only been based on turbines up to 5 MW. With the industry showing rapid growth in turbine and wind farm capacity, further work should be undertaken to verify/tune controller performance for modern-day, high capacity turbines (up to 15MW) and wind farm arrays. Furthermore, this paper will discuss opportunities for utilisation of LIDAR for wind turbine control in the field, its benefits for wind turbine operation and floating substructure design, and the steps needed to be taken to ensure its increased utilisation on industrial projects.