“E+Ǝ” Cores Magnetic Integrated Transformers for Two-Phase Parallel LLC Resonant Converter

An “E+Ǝ” cores two-phase magnetic integrated transformers’ structure is presented. The transformers’ core is assembled with two pieces of “E” core of shorted central legs and one piece of “+” core. The two-phase windings are wound on the upper and lower legs of the “+” core, respectively. The manufactured windings are put around the upper and lower legs of the “+” core very easily. The flux excited by each phase’s windings is separated as two smaller parts, and they pass through the two “E” cores, respectively, which lead to smaller air gap and air-gap fringing flux. The windings do not surround the air gaps, and the air-gap fringing flux does not cause or cause less eddy current loss in windings. The “E+Ǝ” transformers’ magnetic circuit model is established, their parameters are designed, and the losses are calculated. The proposed “E+Ǝ” transformers are verified with simulation and system experiment. Compared with the traditional double “EƎ” transformers, the “E+Ǝ” transformers’ secondary winding length and the corresponding copper loss will increase a little, but their core volume and core loss will decrease more. When a two-phase parallel LLC resonant converter adopts the “E+Ǝ” transformers, its efficiency will increase compared with adopting double “EƎ” transformers.