VUF-Aware Dynamic Operating Envelopes with Coordinated DERs Dispatch and Phase Swapping

Abstract

High penetrations of single-phase photovoltaic (PV) systems and electric-vehicle (EV) chargers in three-phase four-wire low-voltage distribution networks increasingly cause voltage unbalance as measured by the voltage unbalance factor (VUF), which potentially limits distributed energy resource (DER) hosting capacity. This study proposes a VUF-aware, two-stage optimization framework that integrates day-ahead phase swapping and real-time coordinated DER dispatch to expand dynamic operating envelopes (DOEs) under strict power-quality constraints. The operation planning deploys the two-stage framework (Stages I and II) in order to guide local control actions for a real-time operation to mitigate voltage unbalance violations. Stage I uses discrete particle swarm optimization (PSO) to swap the phases of controllable EV chargers and battery energy storage systems (BESS) to pre-balance feeder loading in day-ahead. Stage II applies model predictive control (MPC) based on a linearized three-phase voltage-sensitivity model in every 15 minutes to enforce the operating voltage range in the service level with VUF ≤ 2%. The proposed method is implemented in MATLAB–DIgSILENT PowerFactory co-simulation, and is validated using a 43-bus real-life unbalanced feeder in Pattaya City, Thailand. The results indicate that the proposed method is capable of : (i) reducing the occurrence of VUF-limit violations from 15.18% to 0.36% of all bus–time-step observations, (ii) increasing PV hosting capacity by lowering PV curtailment from 16.15% to 8.14%, (iii) shortening EV charging duration by 32.7%, and (iv) reducing BESS discharge throughput by 45%. Therefore, incorporating VUF as hard constraints within DOEs and co-optimizing phase swapping with real-time P–Q coordination can remarkably enhance power quality, renewable utilization, and EV service without low-voltage distribution network upgrades.