Research on Bidirectional Push-Pull Forward <i>LLC</i> Resonant Converter

In this article, a bidirectional push-pull forward LLC resonant converter is proposed, which is utilized in the electric vehicle, energy storage field, and renewable energy field. The converter is composed of a push-pull forward circuit on the low-voltage side and a voltage doubling rectifier with a resonant tank on the high-voltage side. In addition, to adjust the gain during forward operation, an auxiliary inductor is placed on the high-voltage side. The diodes in the voltage doubling rectifier is replaced by MOSFETs to realize bidirectional power flow. The converter adopts pulse-frequency modulation (PFM). It not only has the advantage of suppressing the voltage spike on the switches, but also enables zero-current switching (ZCS) of rectifier and zero-voltage switching (ZVS) of main switches. A 1 kW experimental prototype is built. The low-voltage side has a voltage range from 48V to 72V, and the high-voltage side is 380V. The highest efficiency of the proposed converter in forward operation is 94.9%, and the maximum efficiency in backward operation is 95.2%.