Admittance Modeling and Application of AC-Side Converters

With the large-scale integration of distributed energy resources, the electrification trend of power systems through power electronics is evident. However, when converters are interconnected with the grid, local grid instability may occur. To address the issue of local instability question, this paper develops an input admittance model for converters that accounts for DC-side voltage fluctuations. By analyzing the impact of current inner loop bandwidth and phase-locked loop(PLL) bandwidth on input admittance, and using the generalized Nyquist stability criterion to study system stability, the accuracy of the model and the correctness of the stability criterion are verified with simulation results. This provides a theoretical basis for designing more stable converter parameters. By comparing models that consider and do not consider DC-side voltage fluctuations, it is found that the former is more accurate. The influence of controller parameters on the admittance model is studied, and the system stability is analyzed using the generalized Nyquist stability criterion, providing a reference for converter parameter design.