Yaw-Augmented Control for Wind Farm Power Tracking

This paper presents a wind farm control strategy to use wake steering (yaw control) to augment pitch control for tracking a power reference signal. The outer loop controller employs a recently proposed dynamic yaw model with a time-varying graph structure that accounts for changes in the farm power output due to the propagation of wakes and wake interactions from yawing turbines. The inner pitch control loop uses a PI controller combined with a novel power-sharing arrangement that reduces the needed derate at each turbine. A compensation scheme accounts for the slow timescale effects of the yaw control actions within the faster timescale pitch control. The controller is applied to track two power trajectories (typical of secondary frequency regulation signals) using a large-eddy simulation wind farm plant. The results demonstrate that the additional control authority from yaw provides some added benefit in reducing the required turbine derates needed for wind farms to track transient power increases in the proposed setting. However, the benefit decreases and pitch control alone is sufficient when the turbines are derated beyond a certain level. These findings suggest that augmenting pitch control with yaw may provide financial incentives in terms of allowing wind farms to maximize power supply to the bulk power market while still providing regulation services. Further work is needed to analyze the costs and benefits of the additional control complexity versus bandwidth in augmenting pitch control with wake steering in these applications.