Transformer Design Technique Based on the Magnetic Equivalent Model of High-Frequency Isolated LLC Converter with High Accuracy and Reduced Design Time

Abstract

High-frequency isolated LLC converters, which require both high efficiency and high density, are gaining important as pivotal technological challenges. In these converters, the transformer plays an essential role not only in providing galvanic isolation between the input and output and in facilitating voltage step-up and step-down but also as a key component in resonance. An appropriate design of the transformer size and structure is required to achieve both high efficiency and high density. This study introduces a self-equivalent magnetic model that incorporates the fringing effect, presenting a design methodology that utilizes this model. Compared with traditional transformer design methods, the proposed methodology allows for a more precise design by considering both the relative permeability and the magnetic path length (MPL), which represents the average path of the magnetic flux. In addition, we employ pareto optimal design techniques to extract a pareto set of transformer designs that satisfy specific conditions and, apply weighting factors to propose an optimal design. The feasibility of the proposed optimal transformer design methodology was verified through finite element analysis simulations and empirical tests using LLC converters.