Reducing Transformer Losses with Adjustable Path-Core Type Inductance in 1.4-MHz LLC Resonant Converters

Path-core type resonant inductance adjustable (PRIA) transformer usage in high-frequency LLC resonant converters is proposed herein to reduce transformer losses. The proposed magnetic structure is a type of transformer with ad-justable resonant inductance combined with a path core for LLC resonant converters. In the proposed transformer, the flux density of the magnetizing inductance can be reduced with a path core. Therefore, fewer core losses are generated when using the proposed transformer. Moreover, the flux of leakage inductance that can be set with the path core has been previously proven by researchers at the Nagoya University laboratory. Consequently, the coil losses, which are one of the largest components of transformer losses, can be reduced effectively by controlling the path of the leakage flux. The proposed PRIA transformer has been reported to improve the efficiency of LLC converters. In this study, a conventional transformer with a magnetic structure is compared with a PRIA transformer through experiments. The core losses were obtained through finite-element simulations, and the coil losses not generated by the magnetic struc-tures were estimated via calculations. The advantage of reducing transformer losses in high-frequency LLC resonant converters with PRIA-structure transformers is presented in this work.