LIDAR-assisted feedforward individual pitch control of a 15 MW floating
offshore wind turbine
Abstract
Nacelle-mounted, forward-facing LIDAR technology is able to deliver
benefits to rotor speed regulation and loading reductions of floating
offshore wind turbines 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 through the use of individual blade pitch
control (IPC). This paper presents a novel LIDAR-assisted feedforward
IPC approach that uses each blade’s rotor azimuth position to allocate
an appropriate individual pitch command from a multi-beam LIDAR. In this
computational study, the source code of OpenFAST wind turbine modelling
software was modified to enable LIDAR simulation and LIDAR-assisted
control. The LIDAR simulation modifications made are present in the
latest OpenFAST release, v3.5. Simulations were performed on a single 15
MW floating offshore wind turbine across the above-rated wind spectrum
and using multiple randomly generated wind profiles. Under a turbulent
wind field with an average wind speed of 17 ms -1, the
LIDAR-assisted feedforward IPC delivered root mean squared error and
standard deviation reductions to key turbine and substructure parameters
by up to 35%. Feedforward IPC delivered enhancements of up to 10% over
feedforward collective pitch control, which instead provided the same
feedforward command to all blades, compared to the baseline feedback
controller. The reductions to the standard deviation and range of the
rotor speed may enable structural optimisation of the tower, while the
reductions in the variations in the loadings present an opportunity for
reduced fatigue damage on turbine components and, consequently, a
reduction in maintenance expenditure.