Developments in inverter technology are resulting in distributed generation units built as a combination of a renewable source or energy storage device and an inverter, and such units are increasingly being used in micro-grids. One advantage of this combination is quick power response, allowing for complex control solutions. This paper presents a control method for battery energy storage systems which minimizes power flow from the utility to micro-grids through an interconnection point, and that limits local bus voltages in middle-voltage 6.6 KV micro-grids, such as those supplied by photovoltaic systems and the utility. Micro-grid loop and radial structures are studied to evaluate the effectiveness of the proposed method. MATLAB/Simulink is used to simulate the micro-grid model using actual photovoltaic data and residential loads from Ota City, Japan.