A Current-Limiting Scheme with Adjustable Virtual Impedance for Three-Phase Four-Wire Grid Forming Inverters

This paper presents a current-limiting scheme for the three-phase four-wire grid-forming inverters. The concept of virtual synchronous generator is employed. The proposed current limitation scheme is applied to each phase independently without interrupting the unfaulty phases. In addition, the current limit in the neutral is taken into consideration. Both virtual inductance and virtual resistance are automatically adjusted based on the amount of overcurrent. To mimic the behavior of a synchronous generator during the occurrence of faults, the cooperation between virtual resistance and inductance is proposed; the virtual resistance provides the fast response against the transient fault current while the virtual inductance is dedicated to limit the steady-state fault current. Simulation results show that the current in each phase is effectively limited for various types of faults in both grid-connected and islanded operations.