Synchronization Stability of Grid-Following VSC Considering Interactions of Inner Current Loop and Parallel-Connected Converters

Abstract

In the grid-following (GFL) voltage source converter (VSC), the synchronization process of phase-locked loop (PLL) can be seriously affected by the interactions from the inner current loop and other parallel-connected VSCs. In this paper, we focus on the influences of these interactions on the synchronization stability of GFL-VSC. Firstly, these interactions are classified into static and dynamic interactions by the mechanism of how they affect the dynamic of PLL. Then, their influence on the synchronization stability is estimated based on a novel Lyapunov stability criterion, which is derived from the extended invariance principle. On this basis, in terms of the physical mechanism, we reveal how the VSC exhibits the non-asymptotic synchronization (i.e., limit cycles) and cascading synchronization instability. In addition, we get the maximum range of static and dynamic interactions that the VSC endure, which can provide the practical design guidance for the VSC. Finally, simulations and experiments are performed to verify the theoretical findings.