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, energy storage system. 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 issue. A switch-controlled auxiliary magnetic inductor branch is added at primary side to have the exact bi-directional voltage gain. Another small inductor is added at secondary side, whose current is easily measured, to control the anti-dc bias. The operation principle, design consideration, and anti-dc bias control strategy are given in this paper. The effectiveness of the proposed method is verified by hardware-in-loop test.