Comparative Evaluation of Three-Phase SiC-Based Voltage/Current-Source Inverter Motor Drives

Variable speed drives (VSDs) operating from a common dc bus enable significant energy savings in variable-load centrifugal systems like pumps and compressors. Ideally, VSDs should provide smooth sinusoidal motor voltages to ensure compatibility with standard motors. Thus, voltage-source inverters (VSIs) equipped with an output filter or current-source inverters (CSIs) are candidate topologies. Using multi-objective Pareto optimization, this paper provides a comprehensive comparative evaluation of VSI and CSI topology and modulation variants, which employ 1200 V and/or 900 V SiC power transistors and drive a 400 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V$</tex> (line-to-line rms), 7.5 kW high-speed permanent magnet synchronous machine (PMSM) with a high nominal output frequency of up to 2 kHz from a 750 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V$</tex> dc bus. The results indicate comparable performance of VSI and CSI topologies in terms of efficiency (weighted according to the NEMA power index load profile) and power density, yet the CSI designs require larger total chip areas at least until 900 V monolithic bidirectional power transistors become available. Advantageously, the CSI's de-side voltage-to-current conversion stage (dc-dc buck converter) can be realized with two interleaved phases that each operate in a triangular-current mode (TCM) and hence with soft-switching, while the dc-link current still shows a low ripple only; this approach clearly outperforms all other considered variants.