Abstract
This project investigates protection coordination during grid-following (GFL) to grid-forming (GFM) transitions in an inverter dominated microgrid that supplies critical loads. A MATLAB/Simulink platform was developed to study delay in GFM switching, feeder pickup sensitivity, main-bus and PCC faults, and mode-aware protection. We found delayed GFM enabling that increases voltage-recovery time and protection risk, while fixed overcurrent settings can lose sensitivity during islanded operation, when the inverter fault current is limited.
Supervisory mode manager and hybrid protection logic were implemented using overcurrent,
undervoltage, frequency, ROCOF, directional, and negative-sequence functions. Public
experimental data from the National Laboratory of the Rockies was used to parallel validate the
GFL/GFM transition and reconnection behavior. The overall evidence suggests that protection
should be designed to adapt to operating mode and transition state rather than rely on a single
fixed relay profile.