Dynamic wind turbine output power reduction under varying wind speed conditions due to inertia

The inertia of wind turbines causes a reduction in their output power due to their inability to operate at the turbine maximum co-efficient of performance point under dynamic wind conditions. In this paper, this dynamic power reduction is studied analytically and using simulations, assuming that a steady-state optimal torque control strategy is used.The concepts of the natural and actual turbine time-constant are introduced, and typical values for these parameters are examined. It is shown that for the typical turbine co-efficient of performance curve used, the average turbine speed can be assumed to be determined by the average wind speed. With this assumption, analytical expressions for the power reduction with infinite and then finite turbine inertia are determined for sine-wave wind speed variations. The results are then generalized for arbitrary wind speed profiles.A numerical wind turbine system simulation model is used to validate the analytical results for step and sine-wave wind speed variations. Finally, it is used with real wind speed data to compare with the analytical predictions. Copyright (c) 2012 John Wiley & Sons, Ltd.