Comparison of Modulation Methods to Reduce the Circulating Current in Paralleled NPC-Converters with Common DC-link

In medium/high power applications including smart transformers, active power filters and wind turbines, parallel converters are a reliable solution to achieve low harmonic distortion, high efficiency and increased power handling. However, if such topology has a common dc-link source, the circulating current arises between the converters, increasing power losses of the switching components and propagating the stress of the dc-capacitors. This paper provides comparison of four most commonly used pulse-width modulation methods and their influence on the circulating current and the quality of the output current. The efficacy of the investigated method is validated by experiments.