Lifetime impact on wind turbine component fatigue of wind farm set-point control dispatch allocation strategies

As wind energy penetration increases in power systems around the world, there will increasingly be times where wind farms will require constraint. At present when constraint is required, wind turbines are often shut down. However, there are significant benefits to curtailing wind farms to a set-point power instead, as a down-rated wind farm can provide grid support services such as frequency support, synthetic inertia and fast acting reserve power. In addition to these benefits to grid stability, curtailing wind farms to a farm wide set-point power output can reduce component fatigue. This paper evaluates the impact on lifetime turbine component fatigue of three different wind farm control strategies for delivering set-point power from a wind farm. This paper uses Strathfarm, a digital twinning wind farm simulation software tool developed by the University of Strathclyde, to simulate a 16 turbine wind farm to analyse the impact of the three allocation strategies on wind turbine component Damage Equivalent Loads (DELs). The considered curtailment allocation strategies are: equally curtailing each turbine within the farm, curtailing based on an approximation of estimated turbine power output (calculated from the wind speed estimate), and a third strategy, called intelligent tower control, which prioritises allocating curtailment to the rated wind speed of the turbine, acting as a strategy of peak shaving at the wind farm level. The intelligent tower control strategy is a novel approach, developed by first considering the steady state loads on the wind turbines in the farm and allocating curtailment to turbines to prioritise curtailment at wind speeds close to the rated wind speed, where tower bending moments are at their highest. Through prioritising curtailment near to the rated wind speed of the turbines, the maximum bending moment of the turbine is reduced which decreases the magnitude of the cycles of the root bending moment of the tower leading to significant reductions in tower DELs.