Experimental Assessment of Induction Motors Fed by Sub-MHz-PWM Wide Band Gap Inverters

Three phase inverters with switching frequencies above 100 kHz have recently become feasible thanks to the significant progress made in wide band gap (WBG) semiconductor technology. The main drivers behind the intense research and development of these ultrahigh switching frequency pulsewidth modulation (PWM) inverters are the extraordinary gravimetric and volumetric power densities that can be achieved. On the other hand, not as much attention has been devoted to the loads that these inverters supply, quite frequently consisting in ac motors. The impact of sub-MHz PWM and of the associated tens of nanoseconds range switching transients on motor terminal overvoltage, common mode currents, and losses are still to be discussed exhaustively. The authors have thus decided to investigate what happens to induction motors (IM) supplied by inverters having switching frequencies up to 350 kHz. After an introduction on WBG semiconductor devices, the article presents some interesting experimental observations conducted on a 1.1 kW four-pole IM fed by a silicon carbide (SiC) inverter. Further insight is provided by tests on a laminated steel toroid, supplied by a single-phase full bridge SiC inverter. Discussions on the experimental results highlight the previously unreported impact of common mode losses, which become a predominant part of the PWM harmonic losses.

Automated summary

Recent progress in wide band gap (WBG) semiconductor technology has made it feasible to have three phase inverters with switching frequencies above 100 kHz, driven by the desire to achieve extraordinary power densities. However, the impact of these inverters on the ac motors they supply has not been extensively discussed. This article investigates the effects of high switching frequency inverters on induction motors, highlighting the previously unreported impact of common mode losses on PWM harmonic losses through experimental observations and tests.