The real drawback of the concept of electrical generator sets (EGS) with variable speed is the engine-generator dynamics at sudden load change from low to high. The analysis of dynamic behavior presented in this paper proves that the disadvantageous dynamical properties of EGS concepts with variable speed of engine can be improved by using an energy storage element. This paper give results of design of the bi-directional dc-dc converters for energy buffer with supercapacitors and also demonstrates the results of dynamic behavior EGS with energy buffer.