Stability Analysis of Grid-connected VSCs Based on Two-port Network Theory

The interactions between voltage source converters (VSCs) and the grid gains as increased attention both in academia and industry, especially frequency-coupled resonances. The frequency-coupling resonances can be described and analyzed using an asymmetrical multiple input multiple output (MIMO) system. The resonance frequency in a MIMO system is hard to identify with conventional impedance matrices when the MIMO system is marginally stable. In this paper, the grid-connected VSC is modeled as a two-port network. By deriving the loop gain of the two-port network with the source and load admittances, a stability analysis method can be proposed, which can identify the resonance frequencies effectively. Simulations and experimental results validate the theoretical analyses.