Microgrids with renewable distributed generation appears to be a good alternative to provide electricity for rural areas and isolated zones. However, these microgrids presents relatively low robustness due to their distributed generation topology with lack of dominant nodes to absorb and compensate instabilities, and intermittent energy availability. This work presents a novel strategy to model microgrids in an extended graph model, generating additional model embedded information, essential for optimization processes in the quest of robustness and economy, among other objectives. The traditional impedance model of microgrid is complemented by an extended graph integrating additional information of grids elements such as saturation, current and voltage limits or energy resource availability. This paper presents the extended graph developed model, which yields to a concise representation of an entire microgrid system, as well as a set of graph metrics usable for electrical grid evaluation. The presented model and metrics show to be useful to store, in a single and simple model, valuable information for design, evaluation and operation of microgrid systems.