Analysis and Reshaping on Impedance Characteristic of DFIG System based on Symmetrical PLL

Heng Nian, Bin Hu, Chao Wu, Yunyang Xu, Frede Blaabjerg

Research output: Contribution to journalJournal articleResearchpeer-review

2 Citations (Scopus)
13 Downloads (Pure)


With the increasing penetration of renewable energy, wind turbines based on doubly fed induction generators (DFIG) are becoming more and more important in the power system. The impedance reshaping control strategy based on the virtual impedance method can be utilized to solve the stability problem of the DFIG-grid interconnected system under the weak grid. However, the stability issues caused by phase-locked loop (PLL) is more complicated due to the frequency coupling characteristic. This article presents an improved control strategy of the DFIG system based on a symmetrical PLL, in which the frequency coupling characteristic can be avoided and the system can be simplified as a single-input single-output system that facilitates the design of virtual impedance. The influence of symmetrical PLL on the operation of the DFIG system is studied, and an improved impedance reshaping control strategy is proposed. Simulation and experimental results are conducted to verify the effectiveness of the proposed impedance reshaping control strategy.

Original languageEnglish
Article number9051649
JournalI E E E Transactions on Power Electronics
Issue number11
Pages (from-to)11720-11730
Number of pages11
Publication statusPublished - Nov 2020


  • Doubly fed induction generator (DFIG)
  • frequency coupling
  • impedance reshaping control strategy
  • symmetrical phase-locked loop (PLL)

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