On the Distance Protection of Power Grids dominated by Grid-forming Inverters

Grid-forming (GFM) inverter architectures have many promising features and offer several advantages over their grid-following (GFL) counterparts in the operation and control of inverter-dominated grids. However, operation of GFM inverters during unbalanced faults and their interaction with existing distance protection have been largely unexplored so far. In this paper, we investigate the performance of traditional distance protection schemes under the GFM paradigm. In particular, we focus on fault-loop impedance computation - which is one of the prevalent functions of contemporary distance protection and fault-zone identification - with different flavours of GFM control architectures. We uncover that GFM control with virtual-impedance limiting yields reliable results for fault-zone identification compared to other alternatives. To validate our analysis and findings, we furnish full-order EMT simulation results as well as experiments on a hardware-in-the-loop (HIL) test bed with a commercial protective relay.