Advanced Primary Control Structure for Variable Speed Wind Turbines with regard to Wind Fluctuations

In the future, wind turbines (WTs) will take part in frequency stabilization by providing inertial and primary power. For the last one a WT must keep power reserves by overspeeding or pitching of the blades and the power output must be varied depending on the grid frequency. The greater the frequency drop is, the higher the power output for the primary control should be. In this paper it is shown that wind fluctuations can cause the drive train to slow down to a standstill during the low-frequency period. This scenario has to be prevented, since the subsequent deactivation of WT generator power can lead to a blackout scenario in the grid. In this publication different control strategies are presented, which are designed to ensure operational stability independent of the considered wind speed curve. The introduced methods are analyzed on the basis of theoretical considerations as well as on simulation and measurement results.