Reproducible Coordinated P--Q Dispatch Optimization of a Smart-Inverter BESS for PV--EV Distribution Networks

This study develops a 24-hour coordinated active- and reactive-power dispatch framework for a battery energy storage system (BESS) interfaced through a four-quadrant smart inverter in a radial distribution network with photovoltaic generation and electric-vehicle charging. The IEEE 33-bus feeder is evaluated under identical operating profiles and fixed hardware for three cases: no BESS, optimized active-power-only dispatch, and coordinated P--Q dispatch. A backward/forward-sweep power-flow solver is integrated with sequential least-squares programming to minimize a normalized objective combining feeder active-energy loss and system-wide voltage deviation, subject to BESS power limits, inverter apparent-power capability, charge/discharge efficiencies, state-of-charge (SOC) bounds, and terminal SOC equality. For an 800-kWh BESS with a 200-kW active-power limit and a 250-kVA inverter connected at Bus~18, P-only dispatch reduces daily feeder loss by 2.65\%, whereas coordinated P--Q dispatch reduces it from 4267.86 to 3842.57~kWh/day, corresponding to a 9.97\% reduction. The coordinated strategy further decreases daily voltage deviation by 17.77\% and improves the worst-case minimum bus voltage from 0.83871 to 0.86695~p.u. The SOC remains within 19.41--95.00\% and returns to 50\% at the end of the scheduling horizon. Under deterministic load, PV, and EV perturbations applied without re-optimization, the fixed P--Q schedule maintains feeder-loss reductions of 9.42--10.61\% and voltage-deviation reductions of 16.48--19.37\%. These results demonstrate the additional network benefit of coordinated reactive-power support while also revealing the practical limitations imposed by fixed inverter capacity.