Dynamic Interaction Analysis of Weak Grid-Tied VSC System in Current Control Timescale

The dynamic interaction among internal components of the grid-tied VSC system can significantly induce instability and endanger the power system. However, the interaction mechanisms within the VSC internal control loops remain obscure, resulting in an unclear identification of the instability evolution process and the dominant element causing system instability. In this paper, a novel model that accurately characterizes the inherent energy evolution of the VSC system is proposed to determine the interaction path and provide clear insights into the vulnerabilities in the system dynamics. First, the Euler-Lagrange dynamic equation of the grid-tied VSC system is established to yield insights into the interaction path from a novel perspective on energy evolution properties. Then, a contribution intensity indicator is proposed for quantifying the contribution of the current control, PLL and grid to VSC system interactions, as well as explaining the interaction process. On this basis, two types of instability in the VSC system are identified, and the effects of various factors on these instabilities are thoroughly analyzed. Furthermore, a data-driven approach is proposed to evaluate the interaction intensity of the VSC system and the participation degree of its subsystems. Finally, the effectiveness of the theoretical analysis results is validated through simulations.