Integrated decouple inductance winding planar transformer for LLC converter

Abstract

The increasing demand for high power density and efficiency in DC-DC converters is proposed the LLC resonant converter as a promising topology for applications such as photovoltaic systems, DC power distribution, and electric vehicle charging. The transformer in LLC converters significantly influences power density, cost, and efficiency, making magnetic design optimization critical. While planar transformers offer advantages like low profile, improved thermal performance, and high power density compared to traditional wire-wound transformers, discrete magnetic components increase system volume, weight, and losses. Magnetic integration, particularly utilizing transformer leakage inductance as a resonant inductor, is a compelling solution to enhance compactness and efficiency. However, existing integration methods face challenges, including insufficient leakage inductance, high core losses, and complex core designs. This paper proposes a novel magnetically integrated LLC resonant converter with decoupled inductor windings that amalgamates resonant and magnetizing inductance within a unified core using a split-integration magnetic flux approach. A detailed analysis of magnetic flux dynamics yields optimized design equations, validated through finite element modeling of flux density and field distribution. Experimental results at 250 kHz resonant frequency and 180 W output power demonstrate the superiority of the proposed design over traditional separate transformers and prior integrated structures with asymmetric windings, achieving improved power density, reduced losses and simplified design procedure.