Capacitor-Voltage Balancing for a Modular Multilevel DSCC Inverter Driving a Medium-Voltage Synchronous Motor

This paper provides a comprehensive discussion on voltage balancing of all the floating capacitors in a modular multilevel cascade inverter based on double-star chopper cells (DSCC) or a modular multilevel DSCC inverter. It intends to use the inverter for driving a medium-voltage synchronous motor. Theoretical and numerical design considerations on both amplitude and phase of the three-phase motor currents achieve better capacitor-voltage balancing in a low-power low-frequency range. A three-phase DSCC inverter with phase-shifted-carrier pulse width modulation is designed, constructed, and tested to drive the 370-V 15-kW 75-Hz six-pole interior-permanent-magnet synchronous motor loaded with a hypothetical centrifugal compressor. Experimental results verify the validity of the theoretical analysis, as well as the effectiveness and viability of the DSCC inverter for such a specific electrical drive.