Hybrid Control for Three-Level LLC Resonant Converter of Dual-Bridge for Wide Output Range

A three-level LLC resonant converter of dual-bridge with hybrid control modulation strategy is proposed for the wide output-voltage range and high input-voltage applications. The topology integrates two neutral-point-clamped arms through an auxiliary transformer, which forms a new controllable double-voltage structure and makes all MOSFETs hold half of the input voltage. Based on the characteristics of the new topology, a hybrid modulation strategy is proposed corresponding to three gain modes, which include conventional pulse frequency modulation and fixed frequency phase shift modulation. Compared to conventional modulation strategies, the proposed hybrid modulation strategy, which improves the output voltage gain range, achieves zero-voltage switching of all the MOSFETs and zero-current switching of rectifier diodes under wider operating voltage and full load range. To minimize the frequency window and improve the efficiency of the converter, the parameter optimization method is designed, which is based on the characteristics of the modulation strategy and the relationship among the maximum output voltage gain, resonant current, and turned- OFF current. At last, the experimental results of the 600-W prototype are presented to confirm the theoretical and characterization analysis.