Grid Impedance Impact Analysis of the Weak Grid-Tied VSC

The grid impedance is widely recognized as the key factor to the stability of the grid-tied power electronic devices. However, the influence of the grid impedance ratio is always neglected due to the assumption that grid reactance is much large than grid resistance. In this paper, it is found that the grid impedance has a different impact on the stability with the reduction of grid impedance ratio. A large grid resistant can improve the stability of the grid-tied VSC due to that the grid resistance can increase the magnitude margin of the grid-tied VSC open-loop SISO transfer functions. Simulations are carried on Matlab/Simulink to verify the effectiveness of the proposed analysis.