I. Introduction
Nowadays, the structure of the power distribution systems has been changed by integrating renewable energy sources and small scale units such as photovoltaic and wind turbines. This resulted in the emergence of “active” distribution systems and microgrids. Microgrids are local networks that involve renewable energy sources and energy storage systems (ESS). They have the capability to be locally controlled. Therefore, they can disconnect from the grid when there is a fault at the main grid, and continue to supply a portion of their local loads in a so called “islanded mode” [1].