LIDAR-assisted feedforward individual pitch control of a 15 MW floating offshore wind turbine

Nacelle-mounted, forward-facing light detection and ranging (LIDAR) technology can deliver benefits to rotor speed regulation and loading reductions of floating offshore wind turbines (FOWTs) when assisting with blade pitch control in above-rated wind speed conditions. Large-scale wind turbines may be subject to significant variations in structural loads due to differences in the wind profile across the rotor-swept area. These loading fluctuations can be mitigated by individual pitch control (IPC). This paper presents a novel LIDAR-assisted feedforward IPC approach that uses each blade's rotor azimuth position to allocate an individual pitch command from a multi-beam LIDAR. In this study, the source code of OpenFAST wind turbine modelling software was modified to enable LIDAR simulation and LIDAR-assisted control. The LIDAR simulation modifications were accepted by the National Renewable Energy Laboratory (NREL) and are now present within OpenFAST releases from v3.5 onwards. Simulations of a 15 MW FOWT were performed across the above-rated wind spectrum. Under a turbulent wind field with an average wind speed of 17 ms-1, the LIDAR-assisted feedforward IPC delivered up to 54% reductions in the root mean squared errors and standard deviations of key FOWT parameters. Feedforward IPC delivered enhancements of up to 12% over feedforward collective pitch control, relative to the baseline feedback controller. The reductions to the standard deviation and range of the rotor speed may enable structural optimization of the tower, while the reductions in the variations of the loadings present an opportunity for reduced fatigue damage on turbine components and, consequently, a reduction in maintenance expenditure.