Low Energy Protection System for DC Grids Based on Full Bridge MMC Converters

Dragan Jovcic, Weixing Lin, Samuel Nguefeu, Hani Saad

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This paper studies protection and control methods for a large DC grid based solely on Full Bridge MMC (Modular Multilevel) converters. An initial theoretical study concludes that DC CB energy dissipation will depend on inductance and square of fault current but not on protection operating time. It is proposed to use differential protection because of robust selectivity and also since it operates well with small series inductors. The analysis of DC CB dissipated energy leads to new protection logic design that delays tripping signals until local current reduces to low values. Low speed DC Circuit Breakers with very small inductors are adequate. The design of controllers for MMC converters should be coordinated with DC grid protection and the study derives values for current controller references. The fault recovery time is found to depend on current reference settings at MMC terminals, and optimal values are derived. The conclusions are confirmed using EMTP simulation on a 400kV, 4-MMC DC grid considering two topologies: with 5 overhead lines and with 5 DC cables.
Original languageEnglish
Pages (from-to)1934-1943
Number of pages10
JournalIEEE Transactions on Power Delivery
Issue number4
Early online date10 Jan 2018
Publication statusPublished - 31 Aug 2018

Bibliographical note

This project is funded by RTE, Paris, France. D. Jovcic and W. Lin are with the School of Engineering, University of Aberdeen, AB24 3UE, U.K. ( d.jovcic@abdn.ac.uk, weixinglin@abdn.ac.uk). S. Nguefeu and H. Saad are with the Réseau de Transport d’Electricité, Paris 92932, France (samuel.nguefeu@rte-france.com, hani.saad@rte-france.com )


  • AC-DC power conversion
  • DC power systems
  • DC power transmission
  • HVDC converters
  • HVDC transmission


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