Stability and mutual effect analysis of the virtual synchronous generator based interconnected AC/DC systems

Virtual synchronous generators (VSGs) are widely utilized in the integration of renewable resources, and the VSG-related small-signal stability is extensively discussed. However, the mutual effect of the AC and DC subsystems on the overall stability of VSG-based interconnected systems is rarely taken into consideration. To address this issue, the hybrid admittance of the VSG containing the AC and DC dynamics is established to capture its coupling characteristics. On this basis, the impedance-based method and determinant properties are introduced to analyze system stability. By defining a relative gain matrix and utilizing the segment amplification and minification, it is theoretically demonstrated that for the interconnecting VSG, the association strength between the mutual effect and system stability experiences a notable reduction as the frequency increases. Specifically, the mutual effect between the AC and DC subsystems of the VSG-based interconnected AC/DC systems can be totally neglected within medium- and high-frequency range. To elucidate further, the stability of the AC and DC subsystems can be investigated independently under this condition, facilitating the model order reduction and stability analysis of the large-scale converter-integrated power systems. Finally, the presented theoretical derivation and analytical expressions are validated through the time-domain and frequency-domain simulations.