Multilevel Inverters for Large Automotive Electric Drives

 Traditional high-frequency pulse width modulation (PWM) inverters for motor drives have several problems associated with their high frequency switching which produces high voltage change (dV/dt) rates. Multilevel inverters solve these problems because their devices switch at the fundamental frequency. Two different multilevel topologies are identified for use as a converter for electric drives, a cascade inverter with separate dc sources and a back-to-back diode clamped converter. The cascade inverter is a natural fit for large automotive electric drives because of the high VA ratings possible and because it uses several levels of dc voltage sources which would be available from batteries or fuel cells. The back-to-back diode clamped converter is ideal for use where a generator or alterntator produces ac voltage. Simulation and experimental results show the superiority of these two converters over PWM based drives.