Simulation study of FACTS devices based on AC-AC modular multilevel hexagonal chopper

Peng Li*, Grain Philip Adam, Derrick Holliday, Stephen Jon Finney, Barry Wayne Williams

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


This study proposes a new range of flexible AC transmission system (FACTS) device based on direct AC-AC conversion, where the modular multilevel AC hexagonal chopper (M2AHC) is employed. The M2AHC is operated in quasi-two-level mode; and the heterodyne modulation is used to decouple voltage amplitude regulation from the phase-shift; thus, independent control of active and reactive powers is achieved. Then, a family of FACTS devices based on M2AHC that offers voltage, active power and reactive power flow control as both shunt and series compensators is analysed. The use of AC cell capacitors instead of DC capacitors in M2AHC makes its footprint much smaller and lighter than conventional AC-DC or DC-AC voltage source converter-based FACTS devices; hence, high reliability and extended service-life could be expected. The system modelling and controller design of the proposed FACTS devices are illustrated in a unified reference frame, considering different control modes, transient and unbalanced conditions. Simulation results are used to verify the feasibility of the proposed M2AHC-based FACTS device. These FACTS devices will be preferred over conventional counterpart for confined spaced applications such as the grid access of large-scale offshore wind farms and resolution of loop flow in megacities.

Original languageEnglish
Pages (from-to)919-930
Number of pages12
JournalIET Power Electronics
Issue number8
Publication statusPublished - 30 Jun 2017


  • flexible AC transmission systems
  • power transmission control
  • power transmission reliability
  • AC-AC power convertors
  • reactive power control
  • load flow control
  • choppers (circuits)
  • voltage control
  • control system synthesis
  • power capacitors
  • M2AHC-based FACTS device
  • AC-AC modular multilevel hexagonal chopper
  • flexible AC transmission system device
  • direct AC-AC conversion
  • quasi-two-level mode
  • heterodyne modulation
  • voltage amplitude regulation
  • active power flow control
  • reactive power flow control
  • shunt compensator
  • series compensator
  • AC cell capacitors
  • controller design
  • system modelling
  • transient condition
  • unbalanced condition
  • large-scale offshore wind farms
  • loop flow


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