Open-end multilevel six-phase machine drive system with three three-leg NPC converters

In this paper, a new multilevel six-phase machine drive system topology is proposed and investigated. The topology is composed of three three-level neutral-point-clamped (NPC) inverters with isolated DC-links feeding the open-end windings (OEW) of a six-phase induction motor (SPIM). The model of the system, operating principles, a space vector pulse width modulation (SV-PWM) strategy, investigation of the harmonic distortion and the common-mode voltage (CMV) generated are presented. The SV-PWM strategy, implemented by means of equivalent level-shifted PWM (LS-PWM), is based on the analysis of three similar individual plans. The used technique allows the generation of multilevel voltage waveforms with reduced switching stress, which is suitable for high power applications which present voltage and current ratings restrictions. The performance of the system is compared with two standard configurations. It has demonstrated some advantages such as: (i) reduced number of isolated DC-link capacitor banks, (ii) lower harmonic distortion of the machine currents, (iii) higher quantity of voltage levels. The feasibilty of the system is demonstrated by simulation and experimental results.