Mathematical Modeling of EMI Spectrum Envelope Based on Switching Transient Behavior

Compared with Si devices, wide bandgap (WBG) devices will cause more serious electromagnetic interference (EMI) problems due to their fast switching speeds. In order to better compare and predict their EMI, this article proposes an improved mathematical modeling method to calculate the EMI spectrum envelope. It is based on an accurate time-domain decomposition of switching transient behavior together with a frequency-domain calculation. Detailed EMI spectrum envelope analytic expressions are derived with full consideration of Miller platform (MP), reverse conduction (RC), and ringing effects, while traditional calculation mainly focused on du/dt. The proposed mathematical modeling method has been applied to Si, silicon carbide (SiC), and gallium nitride (GaN) devices, respectively, and verified by comparing calculated and simulated results. In order to further verify this method, double-pulse test circuits of Si, SiC, emode GaN, and cascade GaN are built, and CM and DM EMI are also compared. The result reveals that, compared with Si devices, the MP, RC, and ringing effects of WBG devices have more serious effects on EMI.