Dual control of active power and Virtual Impedance for Resilient Operation of Grid-forming Inverters During symmetrical Faults

Due to their better performance in maintaining the frequency and voltage stability, grid forming inverters (GFMIs) are promising solutions for the future grid with high penetration of inverter-based resources. Among the GFMIs’ control method virtual synchronous generator (VSG) gained attention because of its closeness to the behavior of synchronous generator. However, limiting the output current of the VSGs during faults while ensuring stable operating condition is challenging especially when multiple GFMIs are connected to the grid. Although the virtual impedance can be designed to decrease the value of the current, the design procedure is performed based on the presumed operating condition which may change due to location and severity of the fault. This paper proposes, a method based on the dual control of input power and virtual impedance during fault which will ensure stable operation of VSGs during fault. According to the grid voltage and the requirements of fault current limiting for VSGs, the virtual impedance is calculated such that the VSG can tolerate fault current. Then, the input power of the VSGs is controlled to reduce the accelerating energy caused by the sudden decrease of grid voltage and output voltage of the VSG. The simulation results are presented to validate the impact of the proposed scheme on maintaining the stability of the VSGs during fault and suppressing fault current.