Stability Analysis of Grid-Connected VSCs Based on S-parameters and Reflection Coefficient

The grid-connected voltage source converter (VSC) is characterized as a multiple-input multiple-output (MIMO) system in the impedance-based stability analysis, which is also a two-port network. In this paper, the stability analysis methods based on electrical characterize description parameters or scattering parameters (S-parameters) and reflection coefficients are compared. Through the use of reflection coefficients, the single-input single-output (SISO) open-loop gains on each bus can be derived individually. The stability can then be analyzed using the classical Nyquist criterion and the relative stability can be defined, as well as the critical bus can be further identified. Moreover, "start-up" resonance frequency can be predicted in the stability analysis. Simulations and the experimental result validate the theoretical derivations.