Minimizing power loss and voltage unbalance in active distribution networks employing multi-objective optimization of voltage regulation equipment and DER re-phasing

The increasing integration of Distributed Energy Resources (DERs) as single-phase units into Active Distribution Networks (ADNs) leads to a rise in Voltage Unbalance (VU) and additional losses. This results in degraded performance of system equipment. Therefore, it becomes essential to minimize VU alongside power losses in ADNs. This paper presents a multi-objective optimization approach based on the coordinated operation of voltage control tools such as Voltage Regulators (VRs), Switchable Capacitor Banks (SCBs), and a re-phasing method for single-phase DERs, to reduce active power losses and VU in ADNs. To achieve this objective, the optimal tap positions of VRs, ON/OFF states of SCBs, and phase configurations for connecting single-phase DERs are determined over a daily operational horizon. Given the random nature and unpredictable behavior of DERs and loads, Hong's 2-point estimation method (H2PEM) is employed to model associated uncertainties. The resulting multi-objective optimization problem is discrete and non-linear; hence, the Discrete Non-Dominated Sorting Genetic Algorithm II (DNSGA-II) is utilized for its solution. An appropriate decision-making criterion is applied to select the optimal solution from the Pareto front. The proposed method is evaluated using modified IEEE 13-bus and IEEE 123-bus ADNs. To assess the effectiveness of the proposed approach, five distinct operational scenarios are investigated. The results show that the proposed strategy reduces active power losses by up to 33.02% and VUF by up to 69.15%, while ensuring that all nodal voltages remain within IEC standard limits. Furthermore, the method utilizes only existing network equipment, making it both practical and cost-effective. These findings validate the technical performance and real-world applicability of the proposed control strategy.