Module-capacitor voltage fluctuation optimization control for an alternate arm converter

Alternate arm converter (AAC) is a recently proposed promising modular multilevel converter. This paper presents a module-capacitor voltage fluctuation suppression strategy based on optimized zero-sequence voltage injection for the AAC. A mathematical analysis for the module-capacitor voltage fluctuation is presented first. Meanwhile, a set of control procedures is designed to synthesize the control of AAC. The proposed strategy can also ensure the zero voltage switching (ZVS) and zero current switching (ZCS) for the director switches which can reduce switching losses and avoid voltage spike across the buffer inductors. The validity of the proposed strategy is verified by simulation studies.