Utilizing Mutual Coupling to Eliminate Parasitic Inductance in EMI Filter Capacitors for Noise Reduction

Power devices based on wide-bandgap (WBG) semiconductor materials, like Silicon Carbide (SiC) and Gallium Nitride (GaN), have notably enhanced power conversion efficiency and power density. However, the fast-switching transient and high switching frequency have brought a significant electromagnetic interference (EMI) challenge within the high frequency (HF) range. And the HF performance of EMI filters is degraded by equivalent series inductance (ESL) of X- and Y-capacitors. In this article, a new and comprehensive model using mutual coupling is proposed to eliminate parasitic inductance for EMI filter capacitors. Based on the proposed model, nine different methods of ESL cancellation are derived. Meanwhile, in contrast to previous research, this work analyzes and compares different ESL cancellation methods. And due to the superiority of symmetrical configuration, it is recommended for ESL cancellation of X-capacitors. In the case studied, the ESL of the X-capacitor has been effectively eliminated up to 40 MHz. Consequently, the differential-mode (DM) noise of the active clamping flyback (ACF) converter exhibits a significant reduction from approximately 3.5 MHz to 30 MHz.