A Bi-Directional DC/DC Converter for an Energy Storage System

This paper addresses a bi-directional dc/dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to one of the dc buses of the dc/dc converter without any chopper circuit. Nevertheless, the dc/dc converter can continue operating when the voltage across the energy storage device droops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc/dc converter. A laboratory model of the energy storage system rated at 200 V and 2.6 kJ designed and constructed in this paper verifies that the dc/dc converter can charge and discharge the capacitor bank properly. Moreover, the dc/dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.