Distance protection of IBR transmission lines considering active voltage support under asymmetrical faults

In the inverter-based resource (IBR) transmission system, the fault ride-through (FRT) control of the IBR significantly modifies its fault characteristics. The existence of transition resistance during faults may result in distance protection mis-operation on the IBR side. Capitalizing on the controllability of IBRs, this paper proposes a control-assistant distance protection method under asymmetrical faults, which achieves dual objectives: active voltage support and transition resistance tolerance. First, an integrated FRT control strategy for IBR that balances point-of-connection (POC) voltage support, fault characterization remodeling, and equipment current limitation is developed. Then, a control-assistant distance protection with strong tolerance to transition resistance is proposed. The protection utilizes the single-terminal sequence components of the transmission line to determine the additional impedance angle of the measured impedance. Further, a unified expression for accurately calculating fault distance is established based on the geometric relation. Finally, the effectiveness of the proposed control-assistant protection is verified in the simulation.