In recent years, distributed generation (DG) and renewable energy source (RES) are attracting special attention to distribution systems. RES such as photovoltaic (PV) system is used as a source of clean energy. However, the large amount of distributed generation causes voltage deviation beyond a statutory range in distribution systems. This paper proposes a methodology for voltage control by using inverters interfaced with DG and tap changing transformers. In the proposed method an one-day schedule of voltage references for the control devices are determined by an optimization technique based on predicted values of load demand and PV power generation. Furthermore, reactive power output are determined according to the locally measurable voltage based on droop characteristic. Slope and reference value on droop characteristic are selected by fuzzy control. The proposed method accomplishes improvement against voltage distribution considering the reactive power output sharing and reduction of distribution loss.