A Time-Sequential Fault Current Limiting Method for Grid-Forming DFIGs in Compliance With Emerging Grid Codes

Abstract

Despite the widespread adoption of grid-forming (GFM) control in inverter-based resources (IBRs), its application in doubly fed induction generators (DFIGs) with simultaneous consideration of modern grid codes (GCs) and fault current limiting (FCL) requirements remains largely unexplored. This paper reveals that the two typical virtual impedance (VI)-based FCL methods designed for GFM-IBRs are ill-suited for GFM-DFIGs during symmetrical faults. This incompatibility is evident not only in the failure to prevent temporary overcurrent but also in the violation of modern GCs regarding the distribution and dynamic response speed of the active and reactive currents. Also, this paper proposes a novel time-sequential FCL strategy to address the demands of both FCL and GC requirements. In this proposed approach, the VI is adaptively adjusted at specific fault stages, while concurrently aligning the internal virtual electromotive force (EMF) of the GFM-DFIG with GC requirements. Simulation results conducted on a 9-bus IEEE test system and hardware-in-the-loop (HIL) testing experiments validate the enhanced alignment with emerging GC standards of the proposed FCL strategy, even under varying symmetrical voltage sags and faulty phase jumps.