Further load reductions with individual pitch control

Previous work has demonstrated that significant reductions in fatigue loading on a wind turbine can be achieved by using individual pitch control, in which the pitch of each blade is adjusted individually, in response to measured loads. The asymmetrical out-of-plane rotor load is measured and an additional pitch action (dominated by the rotational frequency of the rotor) is calculated for each blade in order to minimize this load. This results in the near-elimination of the dominant once-per-revolution ('1P') peak in the out-of-plane load spectrum seen by the rotating components, and fatigue loads can be reduced by 20%-40%. The load reduction is also transferred to the nacelle and tower, but here it is the low-frequency loads which are removed, resulting in a load reduction of a few per cent at best, since the fatigue on the fixed components is dominated by the peak at the blade passing frequency ('3P' for a three-bladed turbine), which is largely unaffected by the individual pitch control action. This article demonstrates a relatively straightforward addition to the individual pitch control algorithm which is capable of reducing the dominant load peak on the fixed components, resulting in significant fatigue load reductions on the whole structure. Copyright (c) 2005 John Wiley & Sons, Ltd.