• Title/Summary/Keyword: Precision control

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Frequency Synchronization of Three-Phase Grid-Connected Inverters Controlled as Current Supplies

  • Fu, Zhenbin;Feng, Zhihua;Chen, Xi;Zheng, Xinxin;Yin, Jing
    • Journal of Power Electronics
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    • v.18 no.5
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    • pp.1347-1356
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    • 2018

  • In a three-phase system, three-phase AC signals can be translated into two-phase DC signals through a coordinate transformation. Thus, the PI regulator can realize a zero steady-state error for the DC signals. In the control of a three-phase grid-connected inverter, the phase angle of grid is normally detected by a phase-locked loop (PLL) and takes part in a coordinate transformation. A novel control strategy for a three-phase grid-connected inverter with a frequency-locked loop (FLL) based on coordinate transformation is proposed in this paper. The inverter is controlled as a current supply. The grid angle, which takes part in the coordinate transformation, is replaced by a periodic linear changing angle from $-{\pi}$ to ${\pi}$. The changing angle has the same frequency but a different phase than the grid angle. The frequency of the changing angle tracks the grid frequency by the negative feedback of the reactive power, which forms a FLL. The control strategy applies to non-ideal grids and it is a lot simpler than the control strategies with a PLL that are applied to non-ideal grids. The structure of the FLL is established. The principle and advantages of the proposed control strategy are discussed. The theoretical analysis is confirmed by experimental results.

  • https://doi.org/10.6113/JPE.2018.18.5.1347 인용 PDF KSCI