Integration of distributed generation (DG) into power systems affects several operating characteristics of the systems including voltage profile and hence voltage stability [1, 2]. However, present trend is to integrate more and more DGs or renewable energy sources into distribution networks and the driving force behind that is mainly the recent advancement in technologies for small-scale power generation using renewable sources. The recent growth in wind and solar energy conversion systems is phenomenon [3, 4]. In fact, a large number of small-scale solar photovoltaic systems and wind generating systems have been connected to distribution systems in recent years.