Current ripple evaluation in dual three-phase inverters for open-end winding EV drives

Ac motor current ripple in electric vehicles is source of electromagnetic interferences and audio noise, from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. A viable solution to reduce the current ripple amplitude is to introduce a multilevel inverter instead of a standard two-level (2L) three-phase inverter. A simple and effective way to achieve a three-level (3L) inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding motor connection. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single 2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole inverter modulation range.