A four-level inverter based drive with a passive front end

Multilevel inverters are suited for high power drive applications due to their increased voltage capability. Specifically, as compared to three level inverters, for a given DC bus voltage, a four-level inverter is able to synthesize better waveforms with reduced device ratings. In a medium voltage drive, a conventional diode bridge rectifier is a low cost multilevel solution if the DC bus voltages can be balanced from the inverter side alone. In this paper, operation of a four-level drive with a passive rectifier is investigated, and modulation constraints of the inverter, arising from the capacitor voltage balancing requirements are examined. Simulation and experimental results are presented to demonstrate the link voltage balancing strategy and the performance of the four-level drive.