A System Representative Model to Study Frequency Excursions in the National Electricity Transmission System and the potential for MT-HVDC Support

  • Nima Mossadegh

Student thesis: Masters ThesisMPhil


Recently, in the UK’s National Electricity Transmission System (NETS), considerable concerns have been raised over the lack of inertia as renewable incentives/targets are rapidly driving future energy mixes towards wind power. Slowly but surely, greater pressures have forced the UK’s Transmission System Operator (TSO), the National Grid Electricity Transmission plc (NGET), to accommodate for weaker sources of inertia, whilst endeavouring to maintain their own system frequency under severe events, in accordance with the Security and Quality of Supply Standard (SQSS) [1]. When predicting the NETS’ frequency response in the so called 2020 “gone green” era [2], the NGET’s Frequency Response Working Group (FRWG) (and various other working groups), developed grid representative models using the Dynamic System Model Approach (DSMA), to predict frequency excursions under a lowered average system inertia. These models were excessively simplified and provided a theoretical estimate on how frequency excursions would pan out following a significant loss in 2020. Furthermore, these existing models ([3] [1] [4] [5]), do not consider the potential quantity of wind connected HVDC links and the wider application of HVDC support for frequency recovery; by means of active power support. So far, Voltage Source Converter (VSC) HVDC technology is seen as a potential option owing to its ability to control reactive and active power independently; furthermore, it is already in use in Two-Terminal (TT) offshore wind parks and interconnectors as seen by Dolwin1 in Germany, and the East-West Interconnector in the UK respectively [6] [7]. Realising its full potential to operate as a MT-VSC-HVDC network, greater potentials were drawn out in this research to overcome the majority of limitations found in TT/MT-Line Commutated Converter (LCC) HVDC, and conventional HVAC networks, in offshore wind park applications.Set by the aforementioned challenges, this thesis therefore improved on the DSMA by building a larger and more detailed System Representative Model (SRM) which permitted accurate frequency response testing in a 2020 setting, and, provided the necessary frequency excursion benchmarks to assess the possibility for MT-HVDC network support. With further detail and accuracy, the SRM provided an invaluable insight into the UK NETS in 2020 and as such led to the recommendations made to counter the lower sources of inertia.
Date of Award5 Nov 2014
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorRaj Aggarwal (Supervisor)


  • Voltage Source Converter
  • HVDC
  • Multi Terminal

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