Study on Transient Stability of Grid-Forming Inverters During Islanded to Grid Connected Mode Transition Embedded with Priority Current Limiter

Conventional transient stability analysis for grid forming inverter from islanded to grid connected mode paid high attention on the nonlinear behavior under different grid strength and different control parameters. However, the grid forming inverter with voltage source nature suffers from the overcurrent risk under large power angle deviation, but the impact of current limiter is overlooked in previous study. Moreover, the nonlinear behavior is overlooked with unknown load. In this paper, the transient stability analysis for grid forming inverter transitioning from islanded to grid connected mode is carried out. It shows that when the resistive-capacitive load that satisfies certain condition will enable the inverter shows totally inverted transient instability or undesired stable operation under current saturation mode risk under same power angle response direction. The findings in this paper provided a physical insight into the nonlinear process of the mode transition and shed light on transient stability improvement design. The findings are verified based on a 500W experimental platform.