Under the condition of a weak grid

the interaction between grid impedance and the control loop of a grid-connected converter will easily trigger wide-frequency oscillation with frequency coupling characteristics. In view of this

this paper takes a three-phase LCL-type grid-connected converter as an example

establishes the dq admittance model of the grid-connected converter

and explores the negative impacts of the asymmetric control loop and grid voltage feed-forward on the stability of the system. Firstly

the decoupling compensation factors are introduced for the asymmetric problem of phase-locked loop and voltage outer loop. Then the compensation matrix is added to the voltage feed-forward path based on the frequency-domain passivity theory. The grid-connected converter is designed as a passive system with single input and single output. Theoretical analysis shows that the proposed method can effectively eliminate the frequency coupling characteristics of the system and control the phase of the converter's sequence admittance in the first and fourth quadrants. The system presents passive characteristics in the full frequency band

which improve the stability of the grid-connected converter under weak grid conditions. Finally

the effectiveness of the proposed approach is verified by simulations and experiments.