Silicon and hybrid Si-SiC tandem inverter analytical loss characterization and comparison to PWM-modulated voltage source inverter

A hybrid silicon (Si)-current source inverter (CSI)/silicon carbide (SiC)-voltage source inverter (VSI) tandem inverter is an appealing combination, synergistically combining relatively low-cost, mature, high current rating Si power switches with the low switching loss, but relatively expensive and current rating limited wide bandgap power (WBG) switches, especially high voltage rated SiC. The tandem inverter structure can be related by analogy to a loudspeaker with a woofer and tweeter, where the woofer (CSI) deals with high-amplitude low frequency output and the tweeter with the low-amplitude high frequency content. Four inverter configurations are investigated: standalone full rated Si-VSI, standalone full rated SiC-VSI, Si-CSI/Si-VSI tandem inverter, and hybrid Si-CSI/SiC-VSI tandem inverter, using analytical loss models and evaluated using commercial power device data. To validate the analytical models, a detailed loss model, implemented in a time-stepping circuit simulation has been employed. The use of selective harmonic elimination optimized pulse patterns in the CSI was also investigated to attempt to reduce the current rating of the VSI in the tandem inverters. Results show that the hybrid Si-CSI/SiC-VSI tandem inverter allows for significantly lower losses for the same load current THD at moderate to high switching frequencies, compared to the standalone Si-VSI. The hybrid Si-CSI/SiC VSI tandem inverter switching frequency range is also extended by at least one order of magnitude compared to Si inverter configurations (potentially allowing for very high output fundamental frequencies) and even beyond the standalone SiC-VSI while using a fraction of the SiC chip area of the standalone SiC-VSI.