Synchronization Stability Analysis of Multi-VSC Grid-Connected System via Multi-Scale Method

In a multiple voltage source converter (VSC) system, the nonlinear characteristics of phase-locked loops (PLLs) and their interactions have a significant influence on the synchronization stability of converters. In this paper, these influences are investigated from the perspective of the time domain. First, a novel time-domain model of the multi-VSC system is obtained by using a multi-scale method. On this basis, a stability criterion is proposed to assess the synchronization stability of the system. Then, the accuracy of the time-domain model and its stability criterion in various conditions are discussed. Moreover, the negative impact of the interaction on the system is quantified. Finally, the above theoretical analysis is also verified in the controller hardware-in-the-loop (CHIL) experiments.