Analysis of subsynchronous control interactions in DFIG-based wind farms: ERCOT case study

In this paper sub-synchronous control interactions (SSCI) in doubly-fed induction generator (DFIG) based wind farms are studied. The SSCI problem has come into prominence since the Electric Reliability Council of Texas (ERCOT) event of 2009, where a faulted line and subsequent outage in the network caused a large DFIG wind farm to become radially connected to the series compensation network, resulting in rapidly increasing sub-synchronous frequency oscillations leading to damage to both the series capacitor and the wind turbine. Therefore, in this paper, the part of the power grid in south Texas that experienced the SSCI in 2009 is considered as a case study. Using eigenvalue analysis on this network the main parameters contributing to the SSCI problem are identified. Finally, a SSCI damping controller (SSCIDC) is designed for this system using observed state feedback controller.