Modal Power Analysis of Complex Circuit for Grid-Connected Converters with Arbitrary Power Factor

When the renewable energy is connected to the weak ac grids, the converter usually needs to operate under non unit power factor to provide reactive power support to the grid, so as to improve the voltage quality of the grid connection point. In order to analyze the stability of grid-connected converter system under non unit power factor conditions, firstly, the primal-dual complex circuit of the system is obtained based on the polar frame impedance modeling, and the modal power of each generalized admittance is calculated. Secondly, the stability of the system is analyzed according to the stability determination method of modal power, the results indicate that modal power is suitable for judging the stability of grid-connected converters with arbitrary power factor. According to the characteristics of the modal power, the influence of the generalized admittance on the oscillation mode is judged, and the critical circuit affecting the system oscillation is divided. Finally, the theoretical analysis results under different control parameters and different power factors are verified by MATLAB/SIMULINK.