Using LIDAR Based Control to Reduce Loads on Floating Wind Turbines and Boost Performance

Abstract

Abstract Offshore wind turbines are being developed worldwide as a large scale source of renewable electricity. However, to accelerate and secure the development in the long term of offshore wind, there is a need to reduce the cost of electricity. To achieve this, wind turbine manufacturers are developing larger size wind turbines, which allow foundation, installation and balance of plant cost reduction. Developing larger wind turbines brings new design challenges, as offshore wind turbines are subject to severe loading resulting mostly from wind speed variation, incoming gusts, and wave loading. The paper presents current developments aiming at reducing loading experienced by offshore wind turbines using advanced control strategies and LiDAR based long-distance wind measurements. In order to mitigate the wind loading, modern wind turbines indeed rely on control systems that define optimal blade pitch positions, in order to reduce the load variation, while optimizing produced electricity. However, most control systems are only based on a feedback from the turbine sensors information, and are therefore limited. In order to overcome this limitation, current developments are being performed to take advantage of additional sensors named LiDAR (Light Detection And Ranging), that can be mounted on the nacelle of wind turbines, and provide long distance wind speed measurements ahead of the wind turbines. Lidars thus provide wind speed measurements at a distance of a few hundred meters, which allow a sufficient reaction time to control the wind turbines. This paper presents new nonlinear strategies that can be used for bottom founded and floating wind turbines, using nacelle-based lidar measurement. Examples are given to highlight the benefits of such strategies, on the wind turbines blades and tower fatigue design. Specific strategies are proposed for floating wind applications and exemplified in the paper, showing a significant load reduction for fatigue and extreme situations. Additionally, production increase can also be obtained. Therefore, these two benefits provide an important contribution to cost reduction of offshore turbines.