Hybrid and modular multilevel converter designs for isolated HVDC–DC converters

I.A. Gowaid, G.P. Adam, Ahmed M. Massoud, Shehab Ahmed, B.M. Williams

Research output: Contribution to journalArticlepeer-review

60 Citations (Scopus)
301 Downloads (Pure)


Efficient medium and high-voltage dc-dc conversion is critical for future dc grids. This paper proposes a hybrid multilevel dc-ac converter structure that is used as the kernel of dc-dc conversion systems. Operation of the proposed dc-ac converter is suited to trapezoidal ac-voltage waveforms. Quantitative and qualitative analyses show that said trapezoidal operation reduces converter footprint, active and passive components' size, and on-state losses relative to conventional modular multilevel converters. The proposed converter is scalable to high voltages with controllable ac-voltage slope; implying tolerable dv/dt stresses on the converter transformer. Structural variations of the proposed converter with enhanced modularity and improved efficiency will be presented and discussed with regards to application in front-to-front isolated dc-dc conversion stages, and in light of said trapezoidal operation. Numerical results provide deeper insight of the presented converter designs with emphasis on system design aspects. Results obtained from a proof-of-concept 1-kW experimental test rig confirm the validity of simulation results, theoretical analyses, and simplified design equations presented in this paper.
Original languageEnglish
Pages (from-to)188-202
Number of pages5
JournalIEEE Journal of Emerging and Selected Topics in Power Electronics
Issue number1
Early online date24 Aug 2017
Publication statusPublished - Mar 2018


  • DC fault
  • dc transformer
  • dc–dc power conversion
  • modular multilevel converter (MMC)
  • dual-active bridge (DAB)
  • power convertors
  • power electronics buildings blocks


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