A modular multilevel converter with ripple-power decoupling channels for three-phase MV adjustable-speed drives

Mohamed S. Diab, Ahmed M. Massoud, Shehab Ahmed, Barry W. Williams

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13 Citations (Scopus)
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This paper presents a drive system based on a modular multilevel converter (MMC) with high-frequency magnetic channels between adjacent-arm submodules (SMs), suitable for medium-voltage, high-power three-phase variable-speed machines. The configuration employs chains of dual half-bridge (DHB) modules linking adjacent SMs of three-phase symmetrical arms. The DHB modules are operating as power channels enabling energy exchange to restore the power imbalance among the SM capacitors. This allows arms' ripple-powers to be entirely decoupled through bidirectional power transfer between adjacent-arm SMs, resulting in a near ripple-free SM capacitor voltage profile. Therefore, the MMC common problem of wide voltage fluctuation across SM capacitors is comprehensively solved, independent of the operating frequency. Additionally, a significant reduction in the sizing requirement of SM capacitance is achieved. The configuration is able to drive multi-megawatt machines from standstill to the rated speed at the rated torque operating condition. The operating principle of the proposed MMC configuration is explained and necessary mathematical analysis is derived. Features and viability of the proposed drive system are verified through simulation and experimentation.
Original languageEnglish
Number of pages15
JournalIEEE Transactions on Power Electronics
Early online date20 Jul 2018
Publication statusE-pub ahead of print - 20 Jul 2018


  • dual half-bridge (DHB)
  • high-frequency transformer
  • low motor speed
  • medium-voltage (MV) variablespeed drives
  • modular multilevel converter (MMC)
  • power decoupling
  • submodule (SM) capacitor voltage-ripple

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