Harmonic Analysis of Input DC Current in Six- and Nine-Phase Voltage Source Inverters

Characterization of the input dc current ripple is imperative for dc-bus capacitor sizing in voltage source inverters (VSIs). While multiphase VSIs are known for their reduced dc current stress, the underlying reason for this reduction is not explored in literature. Furthermore, the effect of winding configuration, namely symmetric vs. asymmetric, was not investigated. This paper presents a detailed harmonic analysis of the input dc current in multiphase inverters, namely six-phase and nine-phase two-level VSIs for the different load configurations. Additionally, benchmarking against three-phase VSIs is conducted to quantify the reduction factor of the current stress in multiphase inverters. It was found that the current stress on the dc-capacitor when supply symmetric six- and nine-phase loads is lower by around 4% when compared to asymmetric loads. The present analysis is validated by simulations and experiments on a six-phase VSI.