Due to the recent significant increase in Distribution Generation technologies and storage such as Solar, Wind and use of electric vehicle batteries improves and widely opens up the high penetration of renewable generation to the grid. The use of renewable distributed generation (DG) technologies and "green power" can provide a significant environmental benefit, and their costs continue to drop. Therefore, utilities try to get more injected renewable energy to our distribution network. However, the integration of such capacity of renewable generations are not beneficial if they are not coordinated properly to work with the prevailing power system grid. This thesis presents an aggregator based optimal power flow method to calculate optimal DG power output, necessary voltages at buses and to control the output of the DGs accordance to the grid behaviors in the distribution system. The proposed method is able to minimize the electricity cost by cutting the power transferred from the grid and to provide the co-optimized operation strategy for distribution system with residential photovoltaics (PVs). A Case study is also presented to demonstrate the feasibility of proposed method.