A Bi-Directional LLC Topology With Symmetrical Gain and Anti-DC Bias Ability

Bi-directional LLC resonant converters play a key role in many critical applications, such as on-board charger and energy storage system. However, for conventional bidirectional LLC converters, the voltage gain becomes narrow and dc bias may occur during reverse operation. Therefore, how to guarantee a symmetrical gain while enabling anti-dc bias ability with minimum cost is a major concern. In this paper, a new bi-directional LLC topology is proposed to address the above issues. Firstly, a switch-controlled auxiliary inductor branch is added at primary side to have the exact bi-directional voltage gain. Secondly, another small inductor is added at secondary side, whose current is easily measured, to control the anti-dc bias. Finally, by adding the dc bias suppression strategy, the proposed topology can ensure the voltage gain symmetrical and have no dc bias problem. Simulation and experiment results demonstrate the effectiveness of the proposed method.