Improved control strategy of mmc–hvdc to improve frequency support of ac system

Zicong Zhang, Junghun Lee, Gilsoo Jang

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


With the continuous development of power electronics technology, variable-speed offshore wind turbines that penetrated the grid system caused the problem of inertia reduction. This study investigates the frequency stability of synchronous, offshore wind-farm integration through a modular-multilevel-converter high-voltage direct-current (MMC–HVDC) transmission system. When full-scale converter wind turbines (type 4) penetrate the AC grid, the AC system debilitates, and it becomes difficult to maintain the AC system frequency stability. In this paper, we present an improved inertial-response-control method to solve this problem. The mathematical model of the synchronous generator is based on the swing equation and is theoretically derived by establishing a MMC–HVDC. Based on the above model, the inertia constant is analyzed using a model that integrates the MMC–HVDC and offshore synchronous generator. With the new improved control method, a more sensitive and accurate inertia index can be obtained using the formula related to the effective short-circuit ratio of the AC system. Moreover, it is advantageous to provide a more accurate inertial control evaluation for AC systems under various conditions. Furthermore, the impact of the MMC–HVDC on system safety is assessed based on the capacitor time constant. This simulation was implemented using the PSCAD/EMTDC platform.

Original languageEnglish
Article number7282
Pages (from-to)1-19
Number of pages19
JournalApplied Sciences (Switzerland)
Issue number20
Publication statusPublished - 2020 Oct 2

Bibliographical note

Publisher Copyright:
© 2020 by the authors. Licensee MDPI, Basel, Switzerland.


  • Effective short circuit ratio (ESCR)
  • Full-scale converter wind turbines (type 4), improved inertia-response control
  • Modular multilevel-converter high-voltage direct-current (MMC-HVDC) transmission system

ASJC Scopus subject areas

  • General Materials Science
  • Instrumentation
  • General Engineering
  • Process Chemistry and Technology
  • Computer Science Applications
  • Fluid Flow and Transfer Processes


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