Comprehensive Analysis and Evaluation of DC-Link Voltage and Current Ripples in Symmetric and Asymmetric Two-Level Six-Phase Voltage Source Inverters

Multiphase drives (MPD) in general and six-phase in particular have been gaining popularity in many industries, which calls for a proper multiphase inverter (MPI) design. For voltage source inverter (VSI)-fed drives, the knowledge of voltage and current stresses on the dc-link are imperative for input capacitor sizing. To this end, the voltage and current stresses on the dc-link capacitor in two-level six-phase VSIs are examined thoroughly in this article for two configurations of load/winding spatial distribution: symmetric and asymmetric. First, the harmonic spectrum of the input dc current of each inverter is analyzed in detail by benchmarking them against the conventional three-phase VSI, to precisely establish the dc-capacitor requirement reduction in six-phase counterparts. Second, analytical formulae for the dc-link capacitor voltage ripples are derived for both configurations. Third, simple formulae for dc-capacitor sizing for six-phase VSIs with different load configurations are provided. The accuracy of the derived formulae is verified by simulation and experimental testing at various power factors and modulation depth. It is found that six-phase VSI supplying symmetric and asymmetric loads reaps 10% and 7% lower dc-link current ripples, respectively. Hence, six-phase symmetric loads yield the smallest capacitor size.