Small Signal Synchronization Stability Analysis of Interconnected System Containing Grid-Forming and Grid-Following Converters from the Perspective of Dual-axis Synchronous Generator

With the integration of large-scale renewable energy sources into the power grid, the interconnection between Grid-Forming (GFM) Voltage Source Converters (VSCs) and Grid-Following (GFL) VSCs has become a prominent trend in the power system. However, significant differences in the synchronization mechanisms between GFM VSCs and GFL VSCs have led to unclear small-signal synchronization stability characteristics in interconnected systems. To address the gap, this paper employs the concept of a synchronous generator that simultaneously controls the dq internal potential components for a better physical understanding, constructing an equivalent structure capable of unifying GFM-VSC and GFL-VSC. Mathematically, a synchronization stability analysis model for interconnected systems based on current sources is established. Furthermore, a quantitative indicator for the small-signal synchronization stability margin in interconnected systems is introduced based on the generalized Nyquist criterion, and a concise analysis is presented regarding the impact of control parameters on small-signal synchronization stability. In addition, an optimization method for GFM-VSCs parameters and configuration based on participation factor iteration is proposed. Finally, simulation examples are built in MATLAB/Simulink to verify the rationality of the theoretical analysis.