Transient Stability Analysis of Paralleled Grid-Following Inverter and Virtual Synchronous Generator Considering Transient Mode Switching

With the rapid evolution of the power system towards a high proportion of renewable energy and a high proportion of power electronics, the grid-following (GFL) inverter and the grid-forming (GFM) inverter have been widely used. However, due to the limited overcurrent capability of the inverter, current limiting measures are usually taken in the GFM inverter, which may cause the GFM inverter to stabilize in current limiting mode without successfully recovering from a fault. In order to understand this phenomenon of the GFM inverter in the parallel system, this paper aims to analyze the fault recovery process of the GFM inverter in the parallel system. First, the mathematical model of the paralleled GFL inverter and GFM inverter system is established, and the virtual synchronous generator (VSG) control is adopted for the GFM inverter. Next, the formula about the output current of the VSG in the parallel system and the output active power of the VSG in current limiting mode are derived. Then the effect of the parameters of the GFL inverter on the mode switching angle of the VSG is analyzed based on the current limiting inequality. Finally, the switching rules are verified by simulation. This paper provides a reference for the parametric design of the GFL- VSG parallel system to improve transient stability when considering current limiting.