Impedance-aware enforcement of transient stability regions for grid-forming converters

As converter technology develops and rated capacities increase, the utilization of converters in power systems is becoming increasingly diverse and expanded. Furthermore, because of the fast control response of these converters, their contribution to power system stability is also increasing. There has been significant research on various approaches to utilizing grid-forming converters beyond microgrids and integrating them into large-scale power systems. In particular, there have been growing concerns about the decrease in stability caused by the low inertia resulting from the high penetration of renewable energy sources. As a possible solution to provide stability improvement, grid-forming converters have been gaining prominence. However, if the strength of the connected system or the angle stability are not considered, there is a possibility of a negative effect on the stable operation of the power system from these grid-forming converters. Therefore, if the topology of the connected system changes because of an event, the performance of the converter needs to be adjusted accordingly. In this paper, an impedance-aware auxiliary protection mechanism is presented for grid-forming converters to ensure stable operation under variations in the connected system impedance. An analysis of the admissible active power operating range based on the system impedance is conducted, and an auxiliary supervisory mechanism is implemented to constrain the converter power reference according to real time impedance variations. • Impedance-aware protection mitigates transient instability of grid-forming converters. • Active power reference is conservatively scaled based on observed impedance increase. • The approach adopts conservative impedance-based criteria for transient protection. • The mechanism relies solely on locally measured voltage and current signals. • Simulation results show enhanced transient stability under topology induced weak grids.