An improved grid impedance estimation technique under unbalanced voltage conditions

Nabil Mohammed, Mihai Ciobotaru, Graham Town

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearchpeer-review

2 Citations (Scopus)


The coupling in synchronous reference frame (dq-axis) of grid-connected inverter reduces the estimation accuracy of grid impedance based on variations of inverter's output power. Therefore, in this paper, an improved grid impedance estimation technique (at fundamental frequency) based on small variations of the inverter's output power is proposed. Moreover, to cope with unbalanced grid voltage conditions, the estimation algorithm is embedded in a positive-and negative-sequence controller (PNSC) strategy. The technique relies on obtaining three operating points produced from a deliberate variations in the dq-current references of the positive-sequence control loop. Adopting three operating points to estimate the grid impedance, significantly reduces the effects of the coupling in the dq-axis during variation of the output power without the need to set either the active or the reactive output power of the inverter to zero during the estimation. Hence, accurate estimation of grid impedance is obtained in a short period of time. Simulation results, using MATLAB\Simulink and PLECS toolbox based on a discrete-time model, show the reliability of the proposed grid impedance technique.

Original languageEnglish
Title of host publicationProceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe)
EditorsVirgil Dumbrava
Place of PublicationPiscataway NJ USA
PublisherIEEE, Institute of Electrical and Electronics Engineers
Number of pages5
ISBN (Electronic)9781538682180, 9781538682173, 97815386821806
ISBN (Print)9781538682197
Publication statusPublished - Sep 2019
Externally publishedYes
EventIEEE/PES Innovative Smart Grid Technologies Europe 2019 - Bucharest, Romania
Duration: 29 Sep 20192 Oct 2019 (Proceedings)


ConferenceIEEE/PES Innovative Smart Grid Technologies Europe 2019
Abbreviated titleISGT Europe 2019
Internet address


  • Grid impedance estimation
  • grid-connected inverter
  • power variations
  • sequences controller
  • unbalance voltage

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