Analysis and Suppression of Common Mode Voltage for SiC Inverters in Electric Vehicle Applications

SiC MOSFETs are expected to replace Si IGBTs in variable-speed motor drives applications for higher power density of inverters, e.g. in electric vehicle(EV), because of their high switching speed, high junction temperature and high blocking voltage. Common-mode voltage (CMV) which would bring common mode electromagnetic interference (EMI) and damage to motor bearings is an important performance index in electric drive system. However, the impact of high switching speed and high switching frequency on common-mode voltage is still ambiguous. In this paper, theoretical analyses are conducted by FFT to study the influence of high switching speed and high switching frequency on CMV and then the experimental verifications are carried out. On this basis, CMV is suppressed by the software and hardware methods. The experimental results show that either has the ability to restrain CMV. But, the best inhibition effect can be achieved by combining both.