Coordination of OLTC and Smart Inverters for Optimal Voltage Regulation of Unbalanced Distribution Networks

TL;DR

This paper presents a novel optimization framework that coordinates smart inverter reactive power and OLTC tap operations to improve voltage regulation in unbalanced distribution networks, reducing deviations and operational costs.

Contribution

It introduces a linearization technique and MILP-based solution for joint control of inverters and OLTCs in unbalanced systems, enhancing efficiency and accuracy.

Findings

Significantly reduces voltage deviations and over-voltage issues.

Decreases unnecessary tap operations and voltage unbalance.

Demonstrates robustness against forecast errors and scalability to large systems.

Abstract

Photovoltaic (PV) smart inverters can improve the voltage profile of distribution networks. A multi-objective optimization framework for coordination of reactive power injection of smart inverters and tap operations of on-load tap changers (OLTCs) for multi-phase unbalanced distribution systems is proposed. The optimization objective is to minimize voltage deviations and the number of tap operations simultaneously. A novel linearization method is proposed to linearize power flow equations and to convexify the problem, which guarantees convergence of the optimization and less computation costs. The optimization is modeled and solved using mixed-integer linear programming (MILP). The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced modified IEEE 37 bus test system and a large California utility feeder. Simulation results show that the proposed method accurately estimates feeder voltage, significantly reduces voltage deviations, mitigates over-voltage problems, and reduces voltage unbalance while eliminating unnecessary tap operations. The robustness of the method is validated against various levels of forecast error. The computational efficiency and scalability of the proposed approach are also demonstrated through the simulations on the large utility feeder.