Long-Term Voltage Stability Analysis of Variable Speed Wind Generators

This paper presents the impacts caused by the integration of variable speed wind turbines on long-term voltage stability. The technologies used are fully rated converter (FRC) and doubly fed induction generator (DFIG) with two control strategies: grid-side converter (GSC) at unity power factor, which is usually adopted, and GSC controlling reactive power. Also, this paper considers wind turbines capability curves and its variable limits, since they are subject to several limitations that changes with the operating point and wind speed. This study also considers the dynamic models of over excitation limiter (OEL) and on-load tap changers (OLTC) combined with static and dynamic loads using time domain simulations. Different penetration levels of wind generation are analyzed. The results show that long-term voltage stability can be improved when GSC of DFIG is controlling reactive power. Moreover, the capability curve plays an important role in this analysis since reactive power is a key requirement to maintain voltage stability.