Efficiency optimisation of a neutral point clamped inverter for electric vehicles by means of a variable DC input voltage and different power semiconductors

The 3-level NPC is investigated for the application in electric vehicles for inverter operation. Two different optimisation approaches for the NPC will be investigated to increase the efficiency. For the first method, the DC link input voltage is controlled variable, fed by a DC/DC converter. The effect of the varied DC link voltage on the loss distribution and on the efficiency is presented. Secondly, the possibility to use IGBTs and Superjunction MOSFETs in one inverter (asymmetric combination) is studied and its effect on the efficiency is highlighted. A continuous and a discontinuous modulation are investigated for the asymmetric combination to show the influence on the loss distribution. Both optimisation methods show advantages regarding the NPC efficiency. The analysis is done by simulation and laboratory measurement.