Dependence of performance of variable speed wind turbines on the turbulence, dynamics and control

Variable speed operation of horizontal axis wind turbines is perceived to have several potential advantages, of which two frequently mentioned ones are the additional energy capture below rated windspeed and the additional power-train compliance and associated load alleviation above rated windspeed. The author highlights that the extent to which the advantages may be realised is dependent on the system dynamics and the turbulence of the wind. If estimates of the benefits are based on static or quasistatic analysis, they may be too optimistic. The dynamics of the wind turbine are determined partly by the control system. The design goals for the control system and its role are clarified in relation to ensuring that maximum benefit is derived from variable speed operation