Multi-cell topologies for three-phase systems operating under unbalanced AC mains and asymmetrical loads

This paper shows two alternatives of a multi-cell converter composed of 3N cells per phase and a multi-pulse power transformer. Both achieve high power quality waveforms in three-phase applications even in the presence of unbalanced AC mains. This is due to the controlled DC link voltage loop. However, under asymmetrical loads just one configuration achieves high performance AC supply currents. The paper reviews both alternatives that use an hysterisis-based DC link voltage control in order to keep an overall unitary displacement power factor. Finally, both configurations are compared by means of simulation where unbalance and distortion indexes are computed.