Analysis and Attenuation of Differential-Mode Resonances due to Winding Capacitances in High-Power Planar Transformers

This paper presents analysis and modeling of differential-mode (DM) resonances due to interactions between inductances and parasitic winding capacitances in high frequency planar transformers, which may result in undesirable current ringing. These DM phenomena are fundamentally different compared to well-recognized and better understood common-mode (CM) issues. A simplified half-circuit model is developed based on the classical six-capacitor network model, and an analytical expression is derived for evaluation of the worst-case differential-mode current ringing. A direct relationship is found between the electric field energy storage and the DM current ringing. The modeling insights lead to improved design approaches for planar transformer and tank inductor windings in transformer isolated converters. The results are verified by experiments on a SiC-based dual-active-bridge converter prototype operating at 9 kW and 210 kHz.