Comparing with centralized large power grid, micro grid is relatively a small sized, regionalized concept. The development of micro grid has a long history, actually, the world’s first DC power plant built by Thomas Edison in 1882 in fact is a micro grid. Recently, micro grid again received spotlight due to the rising awareness of energy saving, carbon reduction, colossal disasters and the trend of renewable energy. In 2000, nations such as the US started to develop micro grid systems that combines renewable energy, which redefined the role of micro grid within the power system.