Cascaded H-bridge Multilevel Inverters -- A Reexamination

Jingsheng Liao
Kai-tak Wan, Missouri University of Science and Technology
Mehdi Ferdowsi, Missouri University of Science and Technology

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Multilevel converters have gained popularity in high-power applications due to their low switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several independent dc sources. Recently, existence of a redundant switching state has been utilized to replace the independent voltage sources with capacitors except for the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, output current of the inverter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This study proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported.