This paper deals with the automatic design of static convertersand electrical machines. Facing the multitude of such devices(converters–machines), the choice of the appropriate converter or machineis a delicate problem. A high level of expertise is required todetermine the best structure for the considered application.This choice could be rapidly made if one had a system which incorporates a greatknowledge of converters, machines and control methods.Firstly, the authors review the realized studies, then they proposethis methodology for a concrete case in order to optimize aninverter–motor of a railway traction chain. Constraints are describedin terms of input and output performances (losses, current, ...).These data are analyzed by using design rules and methods which allow thedecrease of the manufacture cost of the inverter–motor. Rules and methods areimplemented on a workstation by means of an “expert system shell” Smeci.The article proposes several tracks which involve organization, methodology, confirmation and implementation of a tool supporting a method.This process of implementation is the most efficient to fitinto a constant process of improvement which is supported by the returnon experience and by the evolution of the state of the art.