Electromagnetic processes in a bidirectional DC converter with the possibility of increasing and decreasing output voltage levels using an asymmetric inverter for a battery energy storage system when operating in difficult conditions with a short conversion period and determining its parameters are considered. Bidirectional DC converters are widely used in hybrid energy storage systems and in DC distribution power systems. This non-isolated bidirectional boost-buck converter is designed to control the flow of energy between sources with different voltage levels due to the use of low-voltage batteries in these systems. Thanks to the ability of these converters to quickly redirect electrical energy both in one and the other direction, it became possible not only to charge the battery from stationary sources of electricity, but also to charge the battery during the operation of the generator from the internal combustion engine and regenerative braking. The results of calculations of the prototype of a bidirectional DC converter with a 14 V battery, a 200 V DC bus and an output power of 3500 W are given. A prototype was made to confirm the possibility of rapid energy conversion. Ref. 9, fig. 6. Keywords: electric power storage systems, bidirectional DC voltage converter, fast energy conversion, hybrid electric vehicle.