Non-ideal torque control of wind turbine systems: Impacts on annual   energy production
  We discuss non-ideal torque control in wind turbine systems (WTS). Most high-level controllers generate a reference torque which is then send to the underlying electrical drive system (generator+inverter) of the WTS to steer the turbine/generator to its optimal operation point (depending on the wind speed). The energy production heavily depends on the mechanical power (i.e. the product of rotational speed and generator torque). However, since torque sensors in the MW range are not available or extremely expensive, the torque controllers are implemented as feedforward controllers and, therefore, are inherently sensitive to parameter variations/uncertainties. Based on real wind data and a dynamical WTS model, we discuss causes and impacts of non-ideal (feedforward) torque control on the energy production and the gross earnings. 
Christoph M. Hackl and Korbinian Schechner
cs.SY