An Experimental Investigation of the Trade-Off between Switching Losses and EMI Generation with Hard-Switched All-Si, Si-SiC and All-SiC Device Combinations

Silicon carbide (SiC) switching power devices (MOSFETs, JFETs) of 1200 V rating are now commercially available and in conjunction with SiC diodes offer substantially reduced switching losses relative to silicon (Si) IGBTs paired with fast recovery diodes. Low-voltage industrial variable-speed drives are a key application for 1200 V devices, and there is great interest in the replacement of the Si IGBTs and diodes which presently dominate in this application with SiC-based devices. However, much of the performance benefit of SiC-based devices is due to their increased switching speeds (di/dt, dv/dt), which raises the issues of increased EMI generation and detrimental effects on the reliability of inverter-fed electrical machines. In this paper, the trade-off between switching losses and the high frequency spectral amplitude of the device switching waveforms is quantified experimentally for all-Si, Si-SiC and all-SiC device combinations. Whilst exploiting the full switching-speed capability of SiC-based devices results in significantly increased EMI generation, the all-SiC combination provides a 70% reduction in switching losses relative to all-Si when operated at comparable dv/dt. It is also shown that the loss-EMI trade-off obtained with the Si-SiC device combination can be significantly improved by driving the IGBT with a modified gate voltage profile.