After a short historic of the multiphase machines and the state of the art of their open-circuited phase operation, this paper deals with a decoupled three-phase motor drive using a synchronous or induction machine. The modeling of this system uses a vectorial formalism and the energetic macroscopic representation (EMR) applied to normal and open-circuited mode operations. The resultant model is available in the two cases. It is permitted to bring to light the magnitudes evolution and leads to elaborate a "universal" command. This study is achieved with simulation validations, evaluation of the performances and some experimental validations. In conclusion, this method is considered for electrical machines supplied with more than three phases.