Design Methodology for LLC-DCX Converters With High-Power IGBT Modules Considering Dynamic Charge Effects

Abstract

In medium-voltage and medium-frequency (MVMF) applications, LLC dc-dc transformer (LLC-DCX) converters with high-power insulated gate bipolar transistor (IGBT) modules are favored for their compact size, high efficiency, and cost-effectiveness. In these applications, the turn-off behavior of the IGBT is significantly influenced by the dynamic charge stored in the N-base region, which directly affects the turn-off transition time and the associated losses, making traditional LLC-DCX converter design methodologies inapplicable. To address this limitation, this article presents a design methodology that combines a simplified time-domain analytical expression for the resonant current with the IGBT turn-off behavior, resulting in an IGBT turn-off transient model that accurately captures the dynamic charge effects. Based on the IGBT turn-off transient model, a parameter optimization design enables the LLC-DCX converter to operate in discontinuous conduction mode (DCM) with the highest efficiency is carried out. Compared to existing methodologies, this methodology provides a more accurate estimation of the IGBT turn-off transition time and associated losses, enabling precise determination of the maximum magnetizing inductance and the optimal efficiency of the LLC-DCX converter in DCM operation. The effectiveness of the proposed design methodology is experimentally validated using a 9.6-kW LLC-DCX converter.