Multiple-Core Transformer Design Based on Half-Turn Structure in Two-Stage DC-DC Converter for Battery Storage System

This paper aims to design a two-stage Buck-LLC DC/DC converter for battery energy storage system (BESS). Buck converter in the first stage features fast response for regulating, and together with second stage LLC-DCX, high power density and high efficiency can be achieved. To minimize the switching loss and boost the efficiency of GaN devices, dead time and magnetizing inductance are optimized. Moreover, different multiple-core planar transformers are proposed and compared in this paper. To achieve an improved winding design practice, winding loss models are built and simulated based on Finite Element Analysis (FEA). Proposed multiple-core transformer with half-turn structure is verified to be outstanding in eliminating proximity effect which reduces the winding loss by 27% compared to single-core design. A 384 V/12 V 240 W Buck-LLC converter is demonstrated, achieving a peak efficiency of 96%.