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Evaluation of Voltage Unbalance Metrics in Distribution Networks with High DER Penetration

Alireza Zabihi, Luis Badesa, Araceli Hernandez

TL;DR

This paper addresses voltage unbalance in distribution networks with high DER penetration and compares how different definitions—IEC true, NEMA LVUR, CIGRE, and IEEE PVUR1/2—capture the unbalance under realistic loading. It adopts the IEEE European LV test feeder and OpenDSS-based simulations to evaluate index performance and the impact of 40 grid-following PV panels on $VUF$ across three loading scenarios. The results show that the CIGRE/IEC true definition yields exact reflections of $VUF$, LVUR provides a close but sometimes biased estimate, and PVUR1/2 fail to account for phase-angle deviations, reducing accuracy when angles are significant. DER integration can either mitigate or exacerbate $VUF$ depending on DER-load allocation, with PV-based indices improving or degrading accordingly, highlighting the need for robust, accurate voltage-unbalance assessment tools in DER-rich distribution networks.

Abstract

Voltage unbalance, caused by variations in voltage magnitude and phase angle, is a significant power quality issue in three-phase systems, leading to equipment inefficiencies and increased system losses. The integration of distributed energy resources (DER) into the grid adds complexity, as DER can either reduce or worsen voltage unbalance, depending on factors such as grid configuration and the distribution of loads and DER themselves. This study explores the effects of DER penetration on voltage unbalance levels and the accuracy of the different indices most commonly used to quantify this unbalance. The results highlight the varying impacts of DER on unbalance and index performance, emphasizing the need for effective strategies to assess voltage unbalance in modern distribution systems.

Evaluation of Voltage Unbalance Metrics in Distribution Networks with High DER Penetration

TL;DR

This paper addresses voltage unbalance in distribution networks with high DER penetration and compares how different definitions—IEC true, NEMA LVUR, CIGRE, and IEEE PVUR1/2—capture the unbalance under realistic loading. It adopts the IEEE European LV test feeder and OpenDSS-based simulations to evaluate index performance and the impact of 40 grid-following PV panels on across three loading scenarios. The results show that the CIGRE/IEC true definition yields exact reflections of , LVUR provides a close but sometimes biased estimate, and PVUR1/2 fail to account for phase-angle deviations, reducing accuracy when angles are significant. DER integration can either mitigate or exacerbate depending on DER-load allocation, with PV-based indices improving or degrading accordingly, highlighting the need for robust, accurate voltage-unbalance assessment tools in DER-rich distribution networks.

Abstract

Voltage unbalance, caused by variations in voltage magnitude and phase angle, is a significant power quality issue in three-phase systems, leading to equipment inefficiencies and increased system losses. The integration of distributed energy resources (DER) into the grid adds complexity, as DER can either reduce or worsen voltage unbalance, depending on factors such as grid configuration and the distribution of loads and DER themselves. This study explores the effects of DER penetration on voltage unbalance levels and the accuracy of the different indices most commonly used to quantify this unbalance. The results highlight the varying impacts of DER on unbalance and index performance, emphasizing the need for effective strategies to assess voltage unbalance in modern distribution systems.

Paper Structure

This paper contains 12 sections, 22 equations, 8 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Voltage Unbalance Definitions and Comparison
  3. IEC Definition (True Definition)
  4. NEMA Definition
  5. CIGRE Definition
  6. IEEE First Definition (Standard 141)
  7. IEEE Second Definition (Standard 112 and 936)
  8. Comparison
  9. Simulation and Methodology
  10. Integration of PV Panels
  11. Conclusion
  12. Acknowledgement

Figures (8)

  • Figure 1: Load buses of the IEEE European Low Voltage Test Feeder.
  • Figure 2: Buses representing three main distribution zones of the IEEE European low voltage test feeder.
  • Figure 3: Different voltage unbalance indexes in scenario I.
  • Figure 4: Different voltage unbalance indexes in scenario II.
  • Figure 5: Different voltage unbalance indexes in scenario III.
  • ...and 3 more figures