Impedance-based Stability Analysis of AD-DC Hybrid System Considering Grid Impedance

Voltage source converter (VSC) has been widely used as interlinked interface in ac-dc hybrid system. Due to its power electronic characteristics, the interactions between two converters may result in stability issues. There are already many researches on hybrid system stability analysis in both ac and dc sides. This paper mainly focuses on the dc-side stability issue, and investigates the impedance modeling and stability analysis of ac-dc hybrid system with consideration of grid impedance. Based on the developed impedance model and parameter impact analysis, this paper reveals that grid impedance and phase-locked loop (PLL) may influence dc impedance and arouse instability issue in specific condition. Additionally, the impedance model and stability analysis are validated by simulation results.