A Modular Stacked Transformer Structure for LLC Resonant Converters and Analysis of Current Sharing Behavior in Parallel PCB Windings

This paper proposes a modular stacked transformer structure for high-efficiency and high-power LLC resonant converters. Besides the benefits of shrunken footprint and shorten secondary current travelling path that were introduced by the vertically stacked structure, the specific feature of modularity design makes the transformer be simply applied to higher power ratings with high efficiency, high power density and easy fabrication. The design modularity for high power rating extension is demonstrated on a 380 V/12 V 2.4 kW LLC transformer with 4-stack winding PCBs and one core set. Current sharing behavior among all paralleled secondary windings of the proposed stacked structure and its modular design is discussed in terms of the magnetomotive force distribution. The effect of current sharing on winding losses is analyzed and verified using finite element analysis (FEA) simulation. Experimental results show that the LLC converter with the proposed 2.4 kW modular stacked transformer can achieve a peak efficiency of 98.05%.