Enhancement of Small Signal Stability of Multi-Machine System with DFIG using STATCOM

—Integration of DFIG with the multi-machine system causes small signal stability problem i.e., oscillation in the rotor angle and speed of the synchronous machines connected in the multi-machine system due to constant variation in the generation due to uncertain nature of wind. This paper presents a control scheme based on a static synchronous compensator (STATCOM) to enhance the small signal stability of multi-machine system with DFIG by introducing positive damping in the system. A STATCOM operating on a pure voltage control mode does not provide any system damping. However, the STATCOM can contribute to system damping if it is allowed to modulate the bus voltage instead of maintaining it strictly constant. With the introduction of voltage modulating control, the STATCOM transforms the power system into a positively damped system and the eigen values of the system now lies in the left half of the s plane, and any oscillation in the rotor angle and speed will decay with time. The effectiveness of the proposed system is tested in a IEEE -9 bus system using eigen value analysis. Simulation results shows that proposed STATCOM controller is very effective to stabilize the studied system under various disturbances.