Electrical Engineering

, Volume 101, Issue 3, pp 1059–1073 | Cite as

A protection strategy for inverter-interfaced islanded microgrids with looped configuration

  • Hamed Karimi
  • Ghazanfar ShahgholianEmail author
  • Bahador Fani
  • Iman Sadeghkhani
  • Majid Moazzami
Original Paper


Development of an efficient protection strategy is one of the main barriers in paving the way for the implementation of inverter-based microgrids. The limited fault current of voltage-sourced converter (VSC) units as the sole fault feeding sources in the islanded mode of operation makes the fault detection difficult for conventional overcurrent-based protection system. On the other hand, bidirectional power flow due to the presence of distributed energy resource units and looped configuration of microgrids results in miscoordination of the overcurrent relays. To address these problems, this paper proposes a protection strategy for islanded inverter-interfaced looped microgrids. By monitoring the fault-imposed component of VSC current, the proposed scheme quantifies the severity of fault condition as the fault detection criterion. To preserve the protection coordination among available overcurrent relays, the proposed protection scheme adaptively changes the limiting level of hybrid reference frame limiter of the VSC control system proportional to their distances to the fault point. The proposed protection scheme is local, and there is no need for any change in the commercially available overcurrent protection relays. The reliable performance of the proposed protection strategy is assessed on the simulation model of a looped microgrid network.


Distributed energy resource (DER) Fault detection Looped microgrid Overcurrent relay Protection coordination Voltage-sourced converter (VSC) 

List of symbols


Circuit breaker


Current limiting factor


Distributed energy resource


Fault detection index


Hybrid reference frame limiting


Relay current


Plug setting current


RMS value of inductor current reference


Inductor current reference


Limited inductor current reference


Output current


Fault component of output current


Fault-imposed component of output current


Normal-running component of output current


Current threshold


Sampling step


Number of samples within a moving window


Overcurrent relay


Overall severity index


Nominal power of DER


Time delay of Delta filter


Sampling time


Operating time of relay


Amplitude of fault component of DER output voltage


Amplitude of normal-running component of DER output voltage


Nominal voltage of DER


Output voltage


Output voltage reference


Voltage-sourced converter

\(\xi \)

Fault detection threshold



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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Hamed Karimi
    • 1
  • Ghazanfar Shahgholian
    • 1
    Email author
  • Bahador Fani
    • 1
  • Iman Sadeghkhani
    • 1
  • Majid Moazzami
    • 1
  1. 1.Department of Electrical EngineeringNajafabad Branch, Islamic Azad UniversityNajafabadIran

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