Admittance-Based Stability Analysis of Current-Controlled VSG Considering the Frequency Coupling Characteristics

Abstract

Due to the dynamic interaction between the inverter and the grid, the inverter may have power oscillation problems under a weak grid. In this article, considering frequency coupling, the more precise broadband sequence admittance model of the current-controlled virtual synchronous generator (CVSG) is established, and the admittance characteristics of CVSG and traditional grid-connected inverter (TGCI) are compared and analyzed. The amplitude of the sequence admittance of CVSG is generally larger than that of TGCI in the low-frequency region, and in the entire frequency sweep range, the coupling admittance amplitude of CVSG is larger than that of TGCI. In the low-frequency region, the coupling admittance has a great impact on the stability of CVSG and TGCI, so the coupling admittance cannot be neglected when analyzing the stability of the system. The generalized Nyquist stability criterion is used to compare and analyze the influence of power grid strength, phase-locked loop (PLL) bandwidth, and output power on the stability of CVSG and TGCI according to the established admittance model. It can be seen from the stability analysis results that, compared with TGCI, when the PLL bandwidth is relatively large, CVSG has stronger adaptability to the weak grid and power changes. Finally, experiments verify the correctness of the theoretical analysis.