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. A four level inverter is able to synthesize better waveforms and attain higher voltages while reducing the device ratings. While converter device count and kVA are high, a conventional diode bridge rectifier is a low cost multilevel drive solution for the input rectifier if suitable inverter side DC voltage balancing schemes can be devised. This paper investigates the operation of four level rectifier/inverter based drives under commonly used modulation schemes. Link voltage balancing and output voltage capability are analyzed for a four level inverter. Simulation results are presented to verify the link voltage balancing strategy in the absence of any balancing action from the rectifier.