Large Physics experimentation as in particle accelerators or in nuclear fusion is often characterised by a strong and modulated power demand, incompatible with the power availability of the grid. Therefore, large facilities for short-term energy storage have been used, traditionally based on rotating machine. Several new solutions of power supply are studied and especially a new solution for energy storage is presented, where capacitors are used as energy storage elements. They are integrated in the static power converter. The energy- and instantaneous power-demand are presented, and then the global storage system with a dedicated multilevel DC/DC converter with flying capacitors is described. A specific control strategy for voltage balance, together with an adapted loss compensation method is also introduced and developed.