A SOCP-based ACOPF for Operational Scheduling of Three-phase Unbalanced Distribution Systems and Coordination of PV Smart Inverters

TL;DR

This paper introduces a convex SOCP-based ACOPF model for unbalanced three-phase distribution systems, integrating PV smart inverters and Volt-VAr controllers to improve operational efficiency and stability.

Contribution

It develops a novel convex optimization model that accurately characterizes unbalanced networks and co-optimizes inverter settings within standard constraints.

Findings

Effective global optimal solutions for unbalanced systems.

Enhanced system operation through reactive power co-optimization.

Stable system operation verified via time-domain simulations.

Abstract

The proliferation of distributed energy resources (DERs) im-poses new challenges to distribution system operation, e.g., power quality issues. To overcome these challenges and enhance system operation, it is critical to effectively utilize all available resources and accurately characterize unbalanced distribution networks in operational tools. This paper proposes a convex second-order-cone programming (SOCP)-based AC optimal power flow (ACOPF) model for three-phase unbalanced distribution net-works, including smart inverters and Volt-VAr controller (VVC) devices. Reactive power-voltage (Q-V) characteristics of smart inverters of solar photovoltaic (PV) units are also modeled. More-over, the settings of Q-V characteristics of VVC are co-optimized within the proposed ACOPF, considering the allowable range of the IEEE 1547-2018 standard. Furthermore, dynamic analyses are conducted to verify the stability of optimal settings of VVC. The proposed models are tested on an actual 1747-node primary distribution feeder in Arizona. The results illustrate the effective-ness of the proposed ACOPF for unbalanced systems in provid-ing a global optimal solution while capturing the non-linearity and non-convexity of ACOPF. By co-optimizing settings, system operation is improved due to the flexibility of adjusting reactive power output from PV units with VVC. The time-domain simu-lations show that the optimal settings result in a stable system