Partial discharge (PD) activities in wide bandgap (WBG)-based AC machine drives can deteriorate insulation system leading to premature failures, and also affect common-mode electromagnetic interference (CM EMI) noise. To fully understand, detect, and prevent PD activities in the WBG-based AC machine drives with high slew rate, it is critical to measure and analyze a full frequency spectrum of the PD. In conventional PD measurement systems, the full spectrum of the PD cannot be fully captured due to an additional high-pass filter (HPF) with a cutoff frequency higher than 50 MHz, which is commonly used to segregate the PD signal from the switching and EMI noises. The PD activities generally produce a wide frequency spectra including less than 20 MHz range, which can potentially be used for PD detection. In this paper, the full spectra of PD activities during the switching transition of the WBG-based AC machine drive are measured with two different methods without any additional HPF. The measured signals are analyzed in both time and frequency domain to identify major signatures of PD activities in WBG-based AC machine drives.
