Fault Sensitivity Analysis Studies of Grid-Following and Grid-Forming Inverters to Aid System Design

The growing penetration of inverter-based resources (IBRs) in power systems introduces significant challenges to the configuration of distance protection relays which are the mainstay of many protection systems. This study presents a comparative analysis of distance determination with both grid-following (GFL) control configured for fault ride-through (FRT) compliance and grid-forming (GFM) control with a virtual impedance current-limiting. The focusSimulations are carried out at a fixed power set point with variation in fault resistance, fault distance, and the short circuit level (SCL) of the grid. The results highlight the sensitivity of apparent impedance to the fault parameters for the two types of inverters. The findings provide insight into the sensitivities of the fault parameters for each control method, recommending an elongation of the impedance measurement quadrilateral along the resistive axis to improve the performance of distance protection, showing that for varied fault distances the GFM shows a more consistent performance, and demonstrating that the GFM only outperforms the GFL in cases of very high values of grid SCL. This research supports the development of system design practices aligned with the GB grid code and aimed at enhancing protection performance in future power systems.