Journal of Power Electronics

The Korean Institute of Power Electronics (전력전자학회)
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Frequency Synchronization of Three-Phase Grid-Connected Inverters Controlled as Current Supplies

  • Fu, Zhenbin (Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China) ;
  • Feng, Zhihua (Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China) ;
  • Chen, Xi (Department of Substation Maintenance, State Grid Hefei Power Supply Company) ;
  • Zheng, Xinxin (Institute of Automotive Engineering Technology, Hefei University of Technology) ;
  • Yin, Jing (Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China)
  • Received : 2018.01.24
  • Accepted : 2018.05.11
  • Published : 2018.09.20
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Abstract

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.

Keywords

References

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