DC-Link Stability of Stacked Polyphase Bridges Supplying Multiphase Induction Machine Having Common-Duty-Ratio Control

Increasing cost trend for already limited space and land, dictate high-density and high-efficiency as desirable attributes even for medium-voltage (MV) technology. Stacked polyphase bridges (SPB) in combination with multiphase (Nx 3-phase) machine emerges as one of the best fits. It is a transformerless topology, utilizing low voltage semiconductor devices switching at high-frequency, meanwhile exhibiting modularity and redundancy. Amongst different control schemes for SPB, common-duty-ratio (CDR) approach reduces control complexity by eliminating the need for local controllers, which in turn increases system reliability. However, dc-link SPB stability analysis as well as voltage balancing having CDR is not reported in the literature. Analytical analysis, corroborated with simulation and experiments, shows that dc-link dynamics are open-loop stable for multiphase induction machine supplied with SPB having CDR. The CDR control ensures dc-link input voltages balancing and output (ac) current sharing without any active voltage balancing.