In recent years, power variations and energy criteria has been the main motivation for developing regenerative drive converters for elevators . A more performant solution for power-smoothing can be easily found by using a supercapacitor based storage device, connected to the intermediary circuit of a Variable Speed Drive system. In this paper, power and energy considerations are made for the design of the storage tank and regarding the maximum power demand from the feeding network. For the power-conversion circuit, which is necessary to compensate the voltage variations of the supercapacitors by descharging and charging, a high efficiency converter topology is proposed which allows the bidirectionnal energy flow under soft-commutation conditions, and offers also a good flexibility for the optimal sizing of the supercapacitor voltage level. The typical behaviour of the special converter is given, together with an analyse of the advantages related to the specific application.