A soft-switched bi-directional DC-DC converter

High-power, high-frequency and high density bi-directional dc-dc converters are increasingly required in industrial applications and in automotive hybrid-electric power systems. This paper presents detailed analysis and experimental results on a 100 kHz, soft-switched bi-directional dc-dc converter, a novel variation of the auto-transformer soft-switching cell. New closed-form expressions are presented for the average current gain of the converter, taking both the impact of the soft-switching network and the output current ripple into account. These expressions are validated by simulation and experimental results. The efficiency of a prototype converter is shown to be approximately 97% over a wide load range for both buck and boost operating modes. The circuit modes and limitations are discussed. The paper presents a 1 kW experimental comparison between the soft-switched MOSFET- based low-ripple converter, a hard-switched low-ripple IGBT converter and a high-ripple MOSFET converter.