Distributed generation of electric energy has become part of the current electric power system. In this book, a recent research study is arising on a new scenario in which small energy sources make up a new supply system: The microgrid. The most recent research projects show the technical difficulty of controlling the operation of microgrids, because they are complex systems in which several subsystems interact: energy sources, power electronic converters, energy storage systems, local, linear and non-linear loads and of course, the main grid. In next years, the electric grid will evolve from the current very centralized model toward a more distributed one. Summing up, it is pursued the generation of small quantities of electric power by the users (called, microgeneration in the origin), considering them not only as electric power consumers but also as responsible for the generation, becoming this way an integral and active part of the grid.