Effective DC Link Utilization of Multilevel Dual Inverter With Single Source in the Maximal Distention Mode

This paper presents an effective voltage control scheme for an open-end winding (OEW) inverter topology with a single DC supply. The proposed configuration consists of a 3-level flying capacitor inverter at one end, and a floating capacitor fed 2-level inverter at the other end. This dual inverter configuration is operated in the maximal distention mode. i.e., the voltage ratio of the inverters is maintained at 4:1 to get the largest number of effective pole voltage levels. Maximal distention mode has the advantage of good power quality and low voltage stress. A major drawback of open-end winding inverter topology with a single source in maximal distention mode is the inability to charge balance the floating capacitor in the full space vector region, which limits the battery utilization as well as the magnitude of output voltage. In this work, a modified modulation technique is proposed to maintain the floating capacitor at the desired level, attaining a 13.1% increase in the output voltage magnitude, resulting in an improvement in the battery utilization in the same proportion, yielding a smaller and less expensive system. Simulation and experimental results corroborate the proposed modulation technique and voltage control scheme on a 3HP, 3-phase, 415V, 1440 rpm open-end winding induction motor.