A new methodology is presented, based on energy-flow analysis on systems. The aim is to obtain a representation of energy flows between the various sources of a complex system, via energy storage devices connected together with electrical and mechanical converters. Coupling elements can be added to allow the connection of various subsystems. From such a representation, inversion rules lead to the establishment of a maximal control structure that allow an easy identification of the controls needed for the considered system. From this methodology, application example will be given, related to hybrid vehicles.