Design of a Modified Single-Stage and Multistage EMI Filter to Attenuate Common-Mode and Differential-Mode Noises in SiC Inverter

Abstract

The SiC inverter switching at high frequencies introduces increased common-mode (CM) and differential-mode (DM) electromagnetic interference (EMI) issues, such as shaft voltage, bearing currents, insulation degradation, and poor current quality in the motor. These EMI issues are commonly addressed with EMI filters employing CM and DM inductors. The increased volume and poor performance of a CM inductor designed for SiC inverter switching at high frequency require a modified EMI filter design procedure for enhanced performance and volume minimization. In this work, three EMI filters are presented with modified design procedures. A single-stage EMI filter is designed by incorporating a DM filter offering an equal attenuation to DM and CM noise at switching frequency. Here, the additional CM attenuation demand is fulfilled by a marginal value of the CM inductor, while, in multistage EMI filters, the required CM attenuation is split between the two stages. The multistage EMI filter 1 is designed using an additional CM inductor and existing load capacitance as the second stage, whereas the multistage EMI filter 2 is designed with a lesser value of CM inductance to provide CM attenuation over the entire conducted EMI frequency range. The modified EMI filters are tested on an SiC inverter operating at 200 kHz.