Active frequency with a positive feedback anti-islanding method based on a robust PLL algorithm for grid-connected PV PCS

Jong Pil Lee, Byung Duk Min, Tae Jin Kim, Dong Wook Yoo, Ji Yoon Yoo

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)


This paper proposes an active frequency with a positive feedback in the d-q frame anti-islanding method suitable for a robust phase-locked loop (PLL) algorithm using the FFT concept. In general, PLL algorithms for grid-connected PV PCS use d-q transformation and controllers to make zero an imaginary part of the transformed voltage vector. In a real grid system, the grid voltage is not ideal. It may be unbalanced, noisy and have many harmonics. For these reasons, the d-q transformed components do not have a pure DC component. The controller tuning of a PLL algorithm is difficult. The proposed PLL algorithm using the FFT concept can use the strong noise cancelation characteristics of a FFT algorithm without a PI controller. Therefore, the proposed PLL algorithm has no gain-tuning of a PI controller, and it is hardly influenced by voltage drops, phase step changes and harmonics. Islanding prediction is a necessary feature of inverter-based photovoltaic (PV) systems in order to meet the stringent standard requirements for interconnection with an electrical grid. Both passive and active anti-islanding methods exist. Typically, active methods modify a given parameter, which also affects the shape and quality of the grid injected current. In this paper, the active anti-islanding algorithm for a grid-connected PV PCS uses positive feedback control in the d-q frame. The proposed PLL and anti-islanding algorithm are implemented for a 250kW PV PCS. This system has four DC/DC converters each with a 25kW power rating. This is only one-third of the total system power. The experimental results show that the proposed PLL, anti-islanding method and topology demonstrate good performance in a 250kW PV PCS.

Original languageEnglish
Pages (from-to)360-368
Number of pages9
JournalJournal of Power Electronics
Issue number3
Publication statusPublished - 2011 May


  • Anti-Islanding
  • Grid-Connected
  • PLL
  • Photovoltaic PCS

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Electrical and Electronic Engineering


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