Investigation of CM Current Propagation in PEBB 6000: A 10 kV SiC MOSFET-Based Power Electronics Building Block

In this paper, the common-mode (CM) current noise propagation paths in the PEBB 6000 testbed for electromagnetic interference (EMI) characterization are comprehensively investigated to gain a better understanding of noise propagation within and outside the converter. To this end, the 6 kV, 1 MW PEBB 6000 is tested up to 750 kW in DC-DC mode, and CM currents are investigated under two test conditions to examine both the impact of increasing DC bus voltage up to 5 kV and the load current up to 167 A DC. As shown, nearly all the auxiliary power system (APS)-generated noise returns to the APS from the converter aluminum case and does not appear outside the converter. Also, the increase in DC bus voltage directly affects all measured currents, while low-frequency noise components remain unaffected when the load current is increased, except for the return current to the converter case. In contrast, high-frequency noise increases in all paths to some extent due to the faster turn-off transient at higher load currents. Furthermore, low-frequency noise increases drastically in the return current to the converter aluminum frame when the load current increases; when the converter is operating, the current flows from one phase leg to the other through the inductor load. This forms a high di/dt loop that swings in polarity. While it is differential by nature, its magnetic field expands and collapses rapidly, causing the phenomena.