Small boost circuit topology for expanding input voltage range for a bi-directional isolated dc-dc converter

A circuit topology for a bi-directional isolated DC-DC converter and its operation are proposed and evaluation results are discussed. This converter is based on a voltage-source primary circuit and a current-source secondary circuit with an active clamp circuit. To decrease the lower limit of the input voltage for a large voltage range, the proposed topology uses a “small boost circuit” consisting of only a boosting capacitor and a switch on the secondary side. Only when the input voltage is decreased, the switch is kept in the on-state and the secondary voltage is boosted by using transformer series inductance. A 2-kW prototype converter, which has a previously proposed control and the new small boost circuit of the proposed topology, decreased the input voltage lower limit from 289 to 267 V under maximum output conditions.