Gird-connected Inverter Frequency Coupling Elimination and Stability Enhancement Based on Symmetrical PLL Structure Under Weak Grid

In a weak grid with high distributed power generation systems permeability, the grid-connected inverter is prone to frequency-coupled oscillation problems related to the phase-locked loop due to the existence of grid impedance, resulting in reduced gird current quality and grid stability. In order to improve the oscillation suppression capability of the grid-connected inverter, a symmetrical phase-locked loop synchronization structure based on the complex coefficient filter (CCF-SPLL) is proposed. The proposed symmetrical phase locked loop control strategy can avoid the frequency coupling characteristic caused by the traditional phase locked loop without adding additional control compensation loops or adjusting system control parameters, which improves the stability of the grid-connected inverter system in a weak grid environment. Finally, the correctness of the theoretical analysis and the effectiveness of proposed control strategy are verified by the RT-LAB hardware-in-the-loop experimental platform. © 2022 Power System Technology Press. All rights reserved.