A Synchronization Control Technique For Soft Connection of Doubly Fed Induction Generator Based Wind Turbines to the Power Grids

Doubly-fed induction generator (DFIG)-based wind turbine generators need to be connected back to integrated power grid after tripping due to disturbances and emergencies in power grid. Re-connection can cause switching transients which may affect overall grid stability. This situation can be avoided if proper synchronization can be ensured for smooth transition of DFIG from island mode to grid-connected mode. To this effect, in this paper, a direct voltage control based synchronization method is introduced that can ensure low or no transient effect during synchronization of DFIG to the grid. The controller is synthesized based on a multi-channel identification methodology and integrated using a designed grid connection logic for soft synchronization. The architecture is implemented on a modified IEEE 39 bus system with DFIG and tested on a real-time simulation platform with different wind speed conditions. It is observed that the proposed architecture makes the grid more stable (with swings in voltage or frequency reduced as much as 60%) during re-connection of wind generators.