High-Frequency Transformer Based on Parallel Magnetizing Inductor with Reduced Fringing Loss for LLC Resonant Converter

Abstract

This paper proposes a high-frequency transformer based on a parallel magnetizing inductor designed to reduce fringing losses and enable effective heat dissipation. The proposed transformer minimizes fringing losses and achieves high efficiency by employing a structure in which the transformer and inductor are connected in parallel, which makes it possible to reduce the air-gap length while maintaining the optimal turn ratio. Along with reducing the losses, the increased surface area contributes to a better thermal performance. The current applied to the primary side of the proposed transformer is distributed between the transformer and parallel magnetizing inductor, which reduces the thickness of the primary winding and enables the downsizing of the transformer. This compensates for the volume increase caused by the parallel-magnetizing inductor, which prevents a decrease in the power density. A finite element method (FEM) analysis was used to determine the effects of fringing based on the number of turns and identify the point at which losses were minimized, leading to an optimal design. In a design example of a transformer for an LLC converter, the FEM analysis confirmed that the proposed transformer reduced losses by 10.9% compared with a conventionally designed transformer. Experiments were conducted to validate the performance of the proposed transformer.