Abstract
AbstractWith 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 multiblade coordinate (MBC) transformation. This operation transforms and decouples the blade load signals in a yaw‐axis 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 nonrotating 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–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.
Highlights
As wind turbine blades are getting larger and more flexible with increased power ratings, the need for fatigue load reductions is getting ever stronger 1
Individual Pitch Control (IPC) for wind turbine blade fatigue load reductions using the MultiBlade Coordinate (MBC) transformation is widely discussed in the literature 5
The inclusion of an azimuth offset in the reverse MBC transformation is widely applied in literature, up until now, no profound analysis of its implications has been performed
Summary
As wind turbine blades are getting larger and more flexible with increased power ratings, the need for fatigue load reductions is getting ever stronger 1. IPC for wind turbine blade fatigue load reductions using the MBC transformation is widely discussed in the literature 5. Houtzager et al.[16] states that the performance of IPC is reduced by a large phase delay between the controller and pitch actuator, but that the total phase lag of the open-loop system at the 1P and 2P harmonics can be compensated for by including the offset. The authors do not consider the effect of the azimuth offset in their derivation for decoupling of the non-rotating axes, and the resulting possible implementation of IPC with SISO controllers.
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