Characterization and Analysis of Bearing Currents and Shaft Voltages in SiC Inverter Driven PM Machine

The high frequency voltage components generated by pulse width modulated voltages from a variable frequency drive cause voltage build up on the shaft of the inverter-driven machines resulting in bearing damage. Prior work has been done to characterize this phenomenon with several mitigation measures proposed for induction machines. Because the use of permanent magnet (PM) machines is increasing in various applications there are significant research gaps on characterizing shaft voltages and bearing currents in PM machines and their effects on PM machine bearings. This paper presents an investigation of the shaft voltages and bearing currents of PM motors operated with silicon (Si) and silicon carbide (SiC) inverter drives. This paper will characterize, compare, and analyze the differences between the resulting shaft voltage and bearing current of Si and SiC inverters driving induction and PM machines under varying load and temperature conditions.