Reduction of the Circulating Current Among Parallel NPC Inverters

In medium/high power applications, including smart transformers, active filters, and wind turbines, three-level neutral-point-clamped (NPC) inverters proved to be a reliable solution, providing high efficiency low harmonic distortion. practice, several NPCs are parallel connected operated in interleaved manner further increase the handling reduce line filters size. However, if such configuration has common dc-link, high-frequency zero-sequence circulating current (HF-ZSCC) arises among inverters, increasing losses of switching devices propagating stress on dc-capacitors. Moreover, amplitude HF-ZSCC is inversely proportional filter inductance size, therefore real it can reach hundreds amperes even with relatively output currents. The research mostly concentrated two-level for voltage grids traction where size big does not affect system efficiency. Differently, provide higher degree freedom more sophisticated methods applied HF-ZSCC. This article investigates double-reference pulsewidth modulation (DRPWM) as solution diminishing paralleled NPCs. performance DRPWM method confirmed by both simulation experiments, performed 1.6-MVA system.