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

Journal Article · Thu Aug 24 00:00:00 EDT 2017 · IEEE Transactions on Power Electronics

DOI:https://doi.org/10.1109/TPEL.2017.2743780· OSTI ID:1465061

Lu, Maozeng ^[1]; Hu, Jiabing ^[1]; Zeng, Rong ^[2]; Li, Wuhua ^[3]; Lin, Lei ^[1]

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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)

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.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1465061
• Journal Information: IEEE Transactions on Power Electronics, Journal Name: IEEE Transactions on Power Electronics Journal Issue: 7 Vol. 33; ISSN 0885-8993
• Publisher: IEEE
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
capacitor voltage balance
fault ride-through
fundamental frequency reactive circulating current (FFRCC)
high voltage dc (HVDC)
hybrid modular multilevel converter (MMC)