C-LLC-LL resonant converter with wide-gain-range and low-stress for hold-up operation

For applications with hold-up time requirements, the LCLC converter can achieve a wider voltage gain range than the LLC converter without degrading the normal operation efficiency due to its variable-magnetizing-inductor (VML) structure, which is formed by an inductor and an additional capacitor. However, the wide gain range achieved by the VML is at the expense of a high resonant voltage stress of the VML’s capacitor, which affects the converter volume/cost. Hence, to solve the contradiction between wide gain range and low capacitor voltage stress when the VML technique is adopted for hold-up operation, this paper proposes a novel C-LLC-LL converter. Specifically, the VML is arranged into a novel C-dual-LL structure. By relying on the unique output voltages relation between C-dual-LL’s two branches, the reduced voltage stress of the VML’s capacitor and the expanded voltage gain range can be simultaneously realized. To evaluate the feasibility of the proposed solution, a comprehensive analysis is conducted, and experimental results obtained from a 500-W C-LLC-LL prototype are also provided.