Title: Analysis and optimal individual pitch control decoupling by inclusion of an azimuth offset in the multi-blade coordinate transformation,
Abstract: With the trend of increasing wind turbine rotor diameters, the mitigation of
blade fatigue loadings is of special interest to extend the turbine lifetime.
Fatigue load reductions can be partly accomplished using Individual Pitch
Control (IPC) facilitated by the so-called Multi-Blade Coordinate (MBC)
transformation. This operation transforms and decouples the blade load signals
in a yaw- and tilt-axis. However, in practical scenarios, the resulting
transformed system still shows coupling between the axes, posing a need for
more advanced Multiple-Input Multiple-Output (MIMO) control architectures. This
paper presents a novel analysis and design framework for decoupling of the
non-rotating axes by the inclusion of an azimuth offset in the reverse MBC
transformation, enabling the application of simple Single-Input Single-Output
(SISO) controllers. A thorough analysis is given by including the azimuth
offset in a frequency-domain representation. The result is evaluated on
simplified blade models, as well as linearizations obtained from the
NREL~5\nobreakdash-MW reference wind turbine. A sensitivity and decoupling
assessment justify the application of decentralized SISO control loops for IPC.
Furthermore, closed-loop high-fidelity simulations show beneficial effects on
pitch actuation and blade fatigue load reductions.