Comparative Evaluation of Conducted Common-Mode EMI in Voltage-Source and Current-Source Inverters using Wide-Bandgap Switches

Common-mode (CM) voltage and related conducted CM electromagnetic interference (EMI) can cause ground leakage current, motor bearing failures, and audio susceptibility issues in pulsewidth-modulated (PWM) voltage-source inverter (VSI) motor drive applications. When using wide-bandgap (WBG) devices to build motor drive inverters operating at higher switching frequencies, the problems caused by a VSI's CM EMI become more serious. As an alternative, the current-source inverter (CSI) delivers more sinusoidal output voltage waveforms and its dc-link inductor helps to suppress the CM current, making it a promising topology that inherently reduces the motor drive's CM EMI. The conducted EMI generation mechanisms of two-level VSIs and CSIs are evaluated, with detailed discussion of their conducted CM EMI voltage sources and resultant current paths. CM equivalent circuits of both inverters are derived, and the resulting CM EMI transfer functions are employed to assist fast CM EMI estimation and evaluation of means for its suppression. Additionally, the impact of WBG devices and alternative space- vector PWM (SVPWM) strategies on CM EMI are examined.