Stability Analysis on Torsional Interactions of Turbine-Generator connected with DFIG-WECS using Admittance Model

To evaluate the stability of Subsynchronous Torsional Interactions (SSTI), we propose a simple and effective approach using admittance model. The proposed approach gives the subsynchronous conductance based criterion to find the stability of torsional interactions. The subsynchronous conductance based approach is utilized to evaluate the impact of Doubly-Fed Induction Generator based Wind Energy Conversion System (DFIG-WECS) on the torsional vibrations of nearby turbine-generator. The damping of Induction Generator Effect (IGE) and SSTI is analyzed through admittance model at different wind speed with various compensation level. The results of admittance analysis are validated through eigenvalue analysis and transient simulation. The results show that, the DFIG-WECS reduces the damping of torsional modes in the low frequency region of subsynchronous network mode. The damping of SSTI reduces with increase in wind speed. Hence, the DFIG-WECS significantly destabilizes the low frequency torsional modes at high wind speed with high compensation level. Further, it is found that, the network conductance at all critical torsional modes marginally reduces with Subsynchronous Damping Controller (SSDC) at the inner loop of Grid Side Converter (GSC) controller compared to other locations in DFIG converter controllers.