Branch Energy Control of the Three-Phase to Single-Phase Direct AC-AC Modular Multilevel Converter Under Equal Frequency Operation Condition

摘要

For medium- to high-voltage ac-ac conversion applications, direct ac-ac modular multilevel converters (MMCs) show advantages on power density compared to indirect ac-ac (ac-dc-ac) MMCs. However, direct ac-ac MMCs suffer from branch energy divergence when the operation frequencies of the input and the output are equal. This paper investigates the three-phase to single-phase direct ac-ac MMC under equal frequency operation condition and proposes a novel control strategy to balance its branches' energies. The effectiveness of the control strategy is validated by the simulation results.