FACTS Controllers for Grid Connected Wind Energy Conversion Systems

In this paper, the dynamic performance of grid connected wind energy conversion system (WECS) is analyzed in terms of rotor speed stability. The WECS considered is a fixed-speed system that is equipped with a squirrel-cage induction generator. The drive-train is represented as a two-mass model. Results show that for a particular fault simulated, the voltage at the point of common coupling drops below 80% immediately after fault application and exhibits sustained oscillations. The rotor speed of induction generators becomes unstable. In order to improve the low voltage ride-through of WECS under fault conditions and to damp the rotor speed oscillations of induction generator, various flexible ac transmission system (FACTS) controllers such as static VAR (volt ampere reactive) compensator, static synchronous compensator, and unified power flow controller (UPFC) are employed. The gains of these FACTS controllers are tuned with a simple genetic algorithm. It is observed that among the FACTS controllers considered, UPFC is superior not only in regulating the voltage but also in mitigating the rotor speed instability.