Impedance Modeling, Measurement and Stability Analysis of Multi-VSC Systems in αβ Coordinate

Impedance modeling, measurement, and stability analysis of three-phase power converters in alpha beta coordinate have attracted much attention in recent years. This paper revisits and discusses these critical issues. A compact complex vector impedance modeling method is presented for three-phase voltage source converters (VSCs), which avoids complex convolution and matrix operations, thus simplifying the modeling process. Based on the developed model, it is found that linearization at different initial phases of the steady-state trajectories results in different impedance models. The non-uniqueness of the system model not only leads to time dependence on measurements but also plays a critical role in the stability analysis of multi-VSC systems. An accurate and practical measurement-based method is provided to correctly evaluate the stability of systems with multiple converters. Finally, the simulation and control hardware-in-loop (CHIL) experimental results verify the correctness of the theoretical analysis.