Impedance Modeling and Stability Analysis of Weak-Grid Interfaced VSG

Virtual synchronous generator (VSG) is a grid friendly interface owing analogous characteristics to synchronous generator (SG) and is increasingly used in interactive systems like micro-grids. However, the precise impedance features of the VSG, which is regarded as a key point during interactive systems related analysis, has not been figured out at present. In this paper, the complete impedance model of VSG is firstly developed, with the whole power loops taken into consideration. Furthermore, the influence of mirror frequency effect (MFE) is deeply discussed during the impedance modelling. On this basis, an accurate equivalent sequence-impedance model of VSG is provided for on-grid stability analysis with Nyquist criteria. The result shows that VSGs exhibit excellent adaptability in weak grid integration. All these theoretical conclusions are tested and verified via simulations in MATLAB/Simulink eventually.