Analysis and design of a modular multilevel converter with trapezoidal modulation for medium and high voltage DC-DC transformers

I. A. Gowaid, Grain P. Adam, Shehab Ahmed, Derrick Holliday, Barry W. Williams

Research output: Contribution to journalArticlepeer-review

140 Citations (Scopus)
155 Downloads (Pure)


Conventional dual-active bridge topologies provide galvanic isolation and soft-switching over a reasonable operating range without dedicated resonant circuits. However, scaling the two-level dual-active bridge to higher dc voltage levels is impeded by several challenges among which the high dv/dt stress on the coupling transformer insulation. Gating and thermal characteristics of series switch arrays add to the limitations. To avoid the use of standard bulky modular multilevel bridges, this paper analyzes an alternative modulation technique, where staircase approximated trapezoidal voltage waveforms are produced; thus, alleviating developed dv/dt stresses. Modular design is realized by the utilization of half-bridge chopper cells. This way the analyzed dc-dc transformer employs modular multilevel converters operated in a new mode with minimal common-mode arm currents, as well as reduced capacitor size, hence reduced cell footprint. Suitable switching patterns are developed and various design and operation aspects are studied. Soft-switching characteristics will be shown to be comparable to those of the two-level dual-active bridge. Experimental results from a scaled test rig validate the presented concept.
Original languageEnglish
Pages (from-to)5439-5457
Number of pages19
JournalIEEE Transactions on Power Electronics
Issue number10
Early online date5 Dec 2014
Publication statusPublished - Oct 2015


  • DC-DC power convertors
  • modulation
  • alternative modulation technique
  • capacitor size reduction
  • cell footprint reduction
  • electrical stress
  • half-bridge chopper cell
  • high voltage DC-DC transformers
  • medium voltage DC-DC transformers
  • minimal common mode arm current
  • modular multilevel converter
  • staircase approximated trapezoidal voltage waveforms
  • trapezoidal modulation
  • Bridge circuits
  • Capacitance
  • Capacitors
  • Insulated gate bipolar transistors
  • Power transformer insulation
  • Stress
  • Switches
  • DC fault
  • Modular multilevel converter
  • dc fault
  • dc transformer


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