Computer-Aided Design and Optimization of an Integrated Transformer with Distributed Air Gap and Leakage Path for LLC Resonant Converter

Integrating all magnetic elements of an LLC resonant converter into the transformer is not yet fully applied in industry and automotive products. This is due to the fact that conventional integrated transformers often suffer from high winding losses caused by the significant proximity effect. This paper addresses this problem by proposing a combination of a distributed air gap and a leakage path within the transformer. A computer-aided design routine is presented in this paper which allows to find a loss-optimal design using an ETD transformer core. The proposed routine is used to design an integrated transformer of 8 kW operated at 300 kHz which was realized by a custom made ETD core ground out of the favored core material. The low-loss core material and the customized ETD core geometry reduced the transformer volume of a previous integrated design by 30% while keeping its losses equally low.