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Impedance Characteristics Analysis of Modular Multilevel Converter with Direct Modulation and Compensated Modulation

This paper presents a comparative analysis of impedance characteristics of modular multilevel converter (MMC) with direct modulation and compensated modulation. The analytical derivations of the ac-side impedances of the MMC with these two modulation modes are provided, respectively, which are then validated by the measured impedances in the time-domain simulation model. Subsequently, a case study is carried out to show the impact of the two modulation modes on the stability of the MMC-based interconnected system using the impedance-based analysis method. The findings could provide a reference for controller design of MMC-based power electronic systems from a stability perspective.