Conduction Loss Analysis and Optimization Design of Full Bridge LLC Resonant Converter

The operating frequency of LLC resonant converter is usually lower than the resonant frequency to achieve zero current switching of secondary rectifier (ZCS), especially in the heavy load condition, the operating frequency is far less than the resonant frequency. Considering the influence of dead time, the resonant tank current formula derived from the resonant frequency point is different from the actual operating state. To solve this problem, this paper presents an improved current formula of resonant tank, and puts forward a design method of the resonant parameters. Finally, a prototype of 48V input and 1kW/ 400V output is built, and the correctness of the theoretical analysis is verified by simulation and experiment.