Ripple current suppression methods for star-configured modular multilevel converters
The star-configured modular multilevel converter is a promising topology for grid-connected storage as well as power-quality applications and motor drives. During operation, the ac output power generates substantial current pulsation at twice the output frequency in the modules, which causes additional loss and requires an increase of the module capacitance. This paper presents a common-mode voltage injection method that reduces the ripple current by 30%-50% compared to conventional methods under a wide range of load conditions. We further propose to replace the conventional H-bridge modules with double-H-bridge modules, which allow direct power exchange between the arms through the neutral point to smoothen power pulsations. The double-H bridge module can suppress the ripple current by 70%-80%.
