An advanced two-stage grid connected PV system: A fractional-order controller

Shah Fahad, Nasim Ullah, Ali Jafer Mahdi, Asier Ibeas, Arman Goudarzi

Research output: Contribution to journalArticleResearch

9 Citations (Scopus)


© 2019 International Journal of Renewable Energy Research. A fractional-order (FO) based controller for a grid-connected PV system is presented in this paper. A single phase two-stage grid-connected photovoltaic generator (PVG) is used to test the performance of the FO controller. The main objectives of the proposed controller are: (1) To regulate the output voltage of PVG at a point where the maximum power is drawn. (2) Constant DC-link voltage control. (3) Power factor control (PFC) at the inverter output with low total harmonic distortion (THD). To solve the first problem, a non-linear control method known as fractional-order back-stepping control (FOBSC) is used to regulate the output voltage of PVG. A maximum power point tracking (MPPT) technique known as perturb and observe (P & O) is used to generate a reference voltage which is suitable for tracking the maximum power generation of PVG. The generated reference is used to regulate the output voltage of PVG using FOBSC. The DC-link voltage fluctuation issue is tackled using FO based PI controller. The last objective is achieved using FOBSC to obtain maximum power factor of the grid. Lyapunov candidate function is used to verify the stability of the system. To test the performance of the proposed controller, it is compared to conventionally known Integer-order (IO) controller. Results have shown a significant improvement in THD and efficiency of the system. The proposed controller offers 0.94%, 1.43% and 1.86% lower THD in comparison with IO controller at 100%, 80% and 70% of the power generation capacity of PVG, respectively. The overall efficiency of the system for 100%, 80%, and 70% of the dynamic powers of the system is noticed to be better in case of FO controller.
Original languageEnglish
Pages (from-to)504-514
JournalInternational Journal of Renewable Energy Research
Issue number1
Publication statusPublished - 1 Jan 2019


  • Back-stepping control (BSC)
  • Fractional-order (FO)
  • Integer-order (IO)
  • Photovoltaic generator (PVG)


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