In the field of using renewable energy such as the PV system, the batteries are connected to the buses with bi-directional DC-DC converters for ensuring a stable energy supply. Therefore, the bi-directional power conditioners have a key role in renewable power systems. In this paper, bi-directional LLC resonant converter as the power conditioner is proposed. The ac analysis and operating characteristics of bi-directional LLC resonant converter are investigated. Finally, experimental results are shown to confirm the validity of the proposed converter.