A New Optimization Method for Gapped and Distributed Core Magnetics in LLC Converter

Abstract

LLC converter design optimization remains a challenging task for varying loads such as in battery chargers. There are numerous L-L-C combinations to choose from a design space that can satisfy the required voltage gains of the application. An accurate magnetic model is essential to optimally size the passive components according to the application needs. This paper provides a new design tool for gapped core magnetics to optimize the transformer and resonant inductor in LLC converters. Unlike conventional design algorithms, the proposed algorithm considers multiple distributed cores and selects the optimal magnetic flux density by minimizing a penalty function that includes power loss, cost and volume of the magnetic components using Big-Bang Big-Crunch Algorithm. The gapped core transformer and inductor design equations have been verified in Ansys Maxwell and Simplorer co-simulation environment for a 3700 W 48 V LLC and calculated power loss have been compared with experimental results. For the given $L_{m}$ and $L_{r}$ pair of $37.52~\mathrm {\mu H}$ and $9.38~\mathrm {\mu H}$ , the proposed magnetic model designed a transformer with two-distributed cores, each one exhibiting a magnetizing inductance of $17.73~\mathrm {\mu H}$ and leakage inductance of $0.7~\mathrm {\mu H}$ on a EE422120 with 3F36 material. The total power loss of the transformers are measured as 12.44 W on a 3700 W prototype switched at 350 kHz.

Keywords

• Big-bang big-crunch algorithm
• gapped core magnetics
• light electric vehicle
• LLC converter
• LLC transformer optimization
• multi-core LLC transformer