A new current limiting and overload protection strategy for droop-controlled voltage-source converters in islanded AC microgrids under grid faulted conditions

Abstract

Grid-forming voltage source converter (VSC) plays a vital role in the future renewable energy-based utility grid. Limited by the thermal capability of semiconductor switches, grid-forming VSC-based distributed generation units (DGs) cannot stand excess overcurrent like synchronous generators (SG) during large transient disturbances. In order to protect the VSC from overcurrent and ride through the transient disturbances, a new current limiting and overload protection strategy is proposed in this paper. By properly selecting the maximum current thresholds in the synchronous rotating frame, overcurrent and overload protection are achieved simultaneously. The synchronization among DGs is enhanced by feeding back the output voltage in the q-axis to the active power droop control. A comparison study between the proposed strategy and two existing methods are conducted using a networked microgrid in PSCAD/EMTDC, examining the effectiveness of the proposed strategy.