Fault-induced current limitation control for grid-forming inverters: A framework for rapid grid code compliance

Abstract

This paper presents a current limitation scheme for a grid-forming inverter-based resource (IBR). The proposed controller allows the IBR to be integrated into distribution networks while ensuring rapid overcurrent protection and adherence to grid codes for low and medium-voltage grids. The method employs event-triggered time control logic that deactivates grid-forming inverter (GFMI)’s outer power control loop and uses the angle of the current reference as a variable to determine the current injection into the grid during faults. It also monitors the duration the IBR should endure a fault before deciding to trip. The performance of the proposed controller in limiting current is assessed through time-domain simulations after a 100% grid voltage sag. The controller demonstrates a significant improvement in the fault-ride-through (FRT) characteristics and post-fault synchronization dynamics of the GFMI. The study also explores and compares the proposed framework with existing strategies of virtual impedance (VI), current saturation (CS), and priority-based current saturation (PCS). The effectiveness of the proposed controller is also validated through experiments conducted on a power-hardware-in-the-loop (PHiL) test bench that explores the interactions between a physical GFMI and a simulated power grid under various critical operating scenarios like a severe symmetrical fault at the point of common coupling (PCC).