DFIG-based wind energy conversion systems under unbalanced voltage dips

With the uptake of wind power increasing steadily on a global level, the grid compatibility of wind energy conversion systems (WECS) must be improved to ensure that electrical networks with a high wind penetration remain stable and reliable. For this reason WECS must now be able to remain connected to the grid during balanced and unbalanced grid faults and to provide ancillary services such as reactive power support to the grid as stipulated by the grid code requirements. Unbalanced grid voltages can have significant negative effects on the performance of wind energy conversion systems equipped with doubly-fed induction generators. These effects can decrease the lifetime of the system and in extreme cases they can lead to violation of the grid code requirements. In this paper a control strategy is presented, which minimizes torque oscillations and total active power oscillations in the DFIG that arise due to unbalanced voltage conditions in the grid.