Inertia and Frequency Stability Assessment for Renewable-Rich Distribution Feeders

This study evaluates a disturbance-informed, planning-level workflow for assessing steady-state feeder performance and post-disturbance frequency security in renewable-rich distribution networks. The workflow links feeder operation in DIgSILENT PowerFactory to reduced-order frequency-security screening in OpenModelica and PSAT, with Pandapower used as an independent steady-state cross-check. The IEEE 33-bus feeder includes distributed photovoltaic units, DFIG-based wind generation, and a grid-forming battery energy storage system (BESS). Hourly feeder time-series results are used to identify renewable-output deficits, and each deficit is converted from MW to the common 10 MVA dynamic-system base before being applied as a conservative step disturbance. The steady-state validation gives a maximum voltage mismatch of 0.0155 pu, within the adopted 2% screening limit. The cross-tool frequency benchmark shows close agreement for nadir and settling time, while RoCoF is interpreted conservatively because of its sensitivity to numerical differentiation and event implementation. As renewable penetration increases from 0% to 100%, the minimum bus voltage remains close to 1.0 pu (0.9999–0.9991 pu), the maximum bus voltage rises from 1.0295 pu to 1.0826 pu, and feeder losses increase from 0.0246 MW to 0.1531 MW. The 24 h assessment gives a maximum daily voltage of 1.0755 pu at 100% penetration, while loading remains below thermal limits. For the corrected 75% severe event (0.3048 MW; −0.0305 pu on the 10 MVA base), the 2 MW droop-plus-FFR case improves the nadir from 49.9695 Hz without support to 49.9924 Hz. Voltage therefore becomes the earliest binding screening constraint from 50% penetration onward, whereas thermal loading and supported frequency nadir remain non-binding under the studied conditions.