On the impact of the yaw update frequency and wind direction forecasting on open-loop wake steering control

Abstract

When maximizing wind farm power production with wake steering control, the optimal wind turbine yaw misalignment angles depend on the incident wind conditions. In the atmospheric boundary layer (ABL), winds exhibit turbulent fluctuations about temporally evolving mean states. The yaw set-points are updated at some frequency to adapt to these changing conditions, but the best choice for this update frequency, and its dependence on the ABL properties, is unknown. The optimal update frequency must balance adapting the wake steering to the time-varying mean wind conditions against overreacting to turbulence. More frequent updates also increase yaw motor duty and fatigue. We investigate the impact of the yaw update frequency on wind farm energy production and yaw actuator duty, using large eddy simulations of a wind farm operating in the time-varying terrestrial diurnal cycle. We consider open-loop wake steering control approaches which select the yaw misalignment set-points based on either low-pass filtered historical wind conditions or statistical wind condition forecasts. We find that increasing the yaw update frequency does not monotonically increase wind farm energy production – with more frequent updates, the wake steering control is overly reactive to turbulent fluctuations and the wind farm energy is diminished. We characterize the effects of the update frequency depending on the atmospheric stability, and based on the length and time scales of the incident wind.