Mitigating common-mode noise in high frequency LLC resonant converters: a parallel interleaved approach

Abstract

The increasing demands for efficiency and power density in modern applications such as electric vehicles, 5G infrastructure, and data centers have accelerated the adoption of high-frequency DC-DC converters. The use of wide-bandgap semiconductors enables switching frequencies in the megahertz range facilitating the miniaturization of passive components. However, these benefits come with challenges: high dv/dt transitions and parasitic capacitances in planar transformers often result in significant common-mode (CM) noise, leading to electromagnetic interference (EMI). Although conventional mitigation techniques such as structural symmetry, winding balance, and shielding offer partial relief, they frequently necessitate large CM filters. This paper presents an alternative approach by optimizing the magnetic structure and circuit layout of matrix planar transformers to intrinsically suppress CM noise. The proposed methodology is validated through comprehensive high-frequency transformer modeling, circuit-level optimization, and experimental evaluation of a 1 kW GaN-based LLC converter with an input voltage range of 375–405 V and a 48 V output. Results confirm that the proposed design achieves effective CM noise reduction, significantly minimizing the required filter size.