Transient Stability Analysis of Grid-Forming Converter Embedding Adaptive Virtual Impedance as Current Limiting Strategy

Grid-Forming converters may suffer from overcur-rent issues caused by grid voltage sags or faults due to its voltage source characteristics. Adaptive virtual impedance (VI) is a common method to limit the fault currents. However, current limiting strategies constrain the power output capacity and even may cause loss of synchronization. To quantitatively analyse the effect of current limiting strategies on synchronization stability, an accurate power angle characteristic (PAC) is established taking adaptive VI into consideration. Based on the accurate PAC, Lyapunov's direct method and phase portrait method are employed to analyse the transient stability, including the critical clearing time calculation and the region of attraction analysis. Analysis results shows that the accurate PAC helps improve analytical accuracy. Effectiveness of the accurate PAC and theoretical analysis are verified by simulations.