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Title: Imbalance Mechanism and Balanced Control of Capacitor Voltage for a Hybrid Modular Multilevel Converter

Due to different charging and discharging characteristics of full-bridge submodules and half-bridge submodules in hybrid modular multilevel converters (MMC), capacitor voltage imbalance will occur under boosted ac voltage or reduced dc voltage conditions. To address this issue, the mechanism of capacitor voltage imbalance is carefully studied, with three main factors-modulation index, power angle, and hybridization ratio-summarized and their effect on capacitor voltage imbalance analyzed. Further, a control strategy based on fundamental frequency reactive circulating current injection is proposed to keep the capacitor voltage balanced in the hybrid MMC. The amplitude and phase angle of the injected circulating current are calculated and their influence on the energy fluctuation in the submodules' capacitors and the semiconductors' current stress is explored. Lastly, experimental results under boosted ac voltage and reduced dc voltage conditions demonstrate the feasibility and validity of the proposed scheme.
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  1. Huazhong Univ. of Science and Technology, Wuhan (China)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Zhejiang Univ., Hangzhou (China)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
IEEE Transactions on Power Electronics
Additional Journal Information:
Journal Volume: 33; Journal Issue: 7; Journal ID: ISSN 0885-8993
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
Country of Publication:
United States
42 ENGINEERING; capacitor voltage balance; fault ride-through; fundamental frequency reactive circulating current (FFRCC); hybrid modular multilevel converter (MMC); high voltage dc (HVDC)
OSTI Identifier: