Electromagnetic Interference and Partial Discharge Signature Analysis of WBG-Based AC Motor Drives

Exploring high voltage systems with fast-switching wide bandgap (WBG) power devices has shown promise in reducing overall power losses and enhancing performance in electric drives. However, high voltage and high-speed switching also introduce significant challenges, such as partial discharge (PD) and electromagnetic interference (EMI) noise. High-pass filters (HPFs) and high bandwidth current sensors are widely adopted for PD detection to segregate PD signals from common-mode (CM) EMI noise, assuming the PD noise has a higher frequency spectrum than the CM EMI noise. However, a significant drawback remains in the current-based measurement approach, as it does not capture the PD signature within the cut-off frequency range. This paper introduced a voltage-based measurement method that detects a stiff voltage drop due to the PD events. This method is designed to capture the full frequency spectra of PD without additional filtering and interference from CM EMI noise. The measured full frequency range of PD, spanning 4 - 20 MHz, demonstrated a clear comparison in the magnitude of CM EMI noise measured in AC motor drives with and without PD activities (PDs) because the PD conduction path coincides with that of CM EMI noise. As a result, the magnitude of CM EMI noise in both low and high-frequency bands (150 kHz - 1 MHz and 4 - 20 MHz) is observed to be 5 - 10 dBμV higher when PDs are present compared to when they are absent.