A Bidirectional DC–DC Converter for an Energy Storage System With Galvanic Isolation

TLDR

The converter remains operational even as the storage device voltage falls during discharge. The study proposes a bidirectional DC‑DC converter that provides galvanic isolation for energy storage systems. The converter connects an electric double‑layer capacitor directly to its DC side, enabling charge from zero to rated voltage without a chopper or external precharging circuit. Theoretical and experimental analyses show that power loss and peak current constrain the usable DC‑voltage range, and the 200‑V, 2.6‑kJ laboratory prototype confirms correct charging and discharging behavior.

Abstract

This paper addresses a bidirectional 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 a dc side 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 drops 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. Experimental results verify proper charging and discharging operation obtained from a 200-V, 2.6-kJ laboratory model of the energy storage system. Moreover, the dc-dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.