A unidirectional hybrid HVDC transmission system based on diode rectifier and full-bridge MMC

Rui Li, Lie Xu

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)
90 Downloads (Pure)


To reduce the cost of bulk power transmission using voltage source converter HVDC technology, a unidirectional hybrid converter is proposed, where a diode rectifier and a modular multilevel converter (MMC) based on full-bridge (FB) submodules are connected in series on DC side. The FB-MMC controls its DC voltage to regulate the transmitted power. The majority of the power transmission is via the diode rectifier considering its cost and efficiency superiority and only low power rating FB-MMC is required. A thyristor valve is equipped at the DC side of the FB-MMC to prevent potential overcharge of the FB submodules during DC faults. Compared to conventional MMCs, losses can potentially be reduced by around 20%. An active power controller is proposed to regulate the DC voltage of the FB-MMC so as to control the transmitted power. With the inverter station controlling its DC terminal voltage constant, the FB-MMC increases the output DC voltage to increase the transmitted power and, vice versa. To alleviate overvoltage of the HVDC link during AC grid faults of the inverter station, a dynamic DC voltage limiter is designed to actively reduce the DC output voltage of the FB-MMC. Simulation results confirm the proposed converter operation and control.
Original languageEnglish
JournalIEEE Journal of Emerging and Selected Topics in Power Electronics
Early online date10 Aug 2020
Publication statusE-pub ahead of print - 10 Aug 2020


  • active power control
  • diode rectifier HVDC (DR-HVDC)
  • fault ride-through
  • HVDC transmission
  • full-bridge (FB) based modular multilevel converter (MMC)


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