Inverter Impedance Modelling and Stability Analysis Based on Virtual Synchronous Generator Control

The scale of wind/light-based renewable energy grid-connected power generation systems has been expanding. The quantity of solid-state power converters in electrical networks has been growing, leading to grid strength reduction. This presents considerable challenges to the system's operational integrity. In recent years, oscillation accidents of wind/light grid-connected systems under weak grids have occurred frequently, resulting in extremely adverse effects. In order to study this kind of complex oscillation problems, this paper, taking the virtual synchronous generator (VSG)-controlled inverter grid-connected system as the research object, adopts the impedance analysis method and establishes its sequential impedance model. Firstly, the wideband sequence-domain impedance profile of the VSG inverte in the stationary natural coordinate system are established by the sequential impedance modelling method. Secondly, systematic stability characterization of the system is conducted by the Nyquist criterion and the Bode criterion. The consequences of grid impedance variations change on the dynamic stability of the system is specifically analyzed. Finally, The validity of the analytical treatment is confirmed through time-domain simulation based on the PSCAD/EMTDC electromagnetic transient platform. The study shows that the VSG-controlled inverter can maintain sufficient phase margin under weak grid conditions and has a strong adaptive ability to the weak grid. This paper contributes a theoretical basis for the choice of control strategy and stability analytical method for renewable energy grid-connected inverters under weak grid conditions.