The paper proposes a methodology to define the architecture of the power unit of a UFC (Ultra Fast Charging) station for electric vehicles (EVs), capable of reaching a power of 350 kW. The main goal is to improve the efficiency of the system defining the best configuration by a MATLAB software (BEA – Best Efficiency Architecture) developed by the authors. The software allows defining the best architecture taking into account efficiency-power curves of all AC/DC and DC/DC power modules currently available on the market, thus increasing energy savings. Architectures based on different connection of AC/DC and DC/DC converters using DC bus have been taken considered. The best configuration found has been simulated using Simulink software, performing time-domain electrical simulations in order to verify and validate the architecture chosen.