Hybrid bidirectional AC/AC multilevel converter

摘要

A new bidirectional multilevel converter topology called Hybrid Multilevel Converter (HMC) suitable for high power AC/AC applications is presented. It is based on cascaded connection of multiple half-bridge submodules in addition to nine thyristor-based low-frequency and soft-switched unfolders in a three-phase version. Compared with a conventional modular multilevel converter (MMC), HMC requires less number of capacitors and IGBTs and also does not inherit the internal unwanted circulating current which obviates the necessity of arm inductors. A control strategy is developed which guarantees the capacitor voltage balancing in different operating conditions. The practicality of the modified SMMC, as well as the effectiveness of the voltage balancing control, is confirmed by simulation.