Investigation of fault ride-through behavior of DFIG-based wind energy conversion systems

Asymmetrical voltage conditions in the grid can have significant negative effects on the performance of wind energy conversion systems (WECS) equipped with doubly-fed induction generators (DFIG). Transient peaks as well as steady-state second-order and higher frequency harmonics are introduced in the active and reactive output powers, in the DC-link voltage and in the toque produced by the WECS. These effects can decrease the lifetime of the system and in extreme cases they can lead to violation of the grid code requirements as the system will not be able to ride-through the fault. Protective measures must be taken so that the WECS remains connected to the grid and fulfills the low voltage ride-through requirements, without putting the reliability of the system at risk. In this paper the dynamic behavior of the DFIG-based WECS in the case asymmetrical voltage dips is analyzed. A control strategy is presented, which minimizes the negative effects of voltage dips on the WECS and enables it to `ride-through´ the fault safely. With this strategy the wind energy conversion system can support the voltage recovery during and after the fault and it can fulfill the demanding grid code requirements.