Applicability of true voltage unbalance approximation formula for unbalance monitoring in LV networks with single-phase distributed generation

Abstract

In the hierarchy of power transmission and distribution systems, the three-phase LV distribution networks are most susceptible to voltage unbalance (VU). The main causes are large presence of randomly distributed single-phase loads and, following the latest trends, the increasing presence of single-phase distributed generators. Most widely accepted VU calculation is based on percentile ratio of negative and positive sequence voltage (voltage unbalance factor, VUF). Obtaining sequence voltages is a complex domain calculation and requires simultaneous sampling of three-phase voltages and angles. This is why the existing VU monitoring and mitigation solutions are dominantly three-phase. Without an additional three-phase aggregation device, there is an inherent gap in VU monitoring for single-phase loads and generators. In this paper, the data concentrators for a growing PV micro-inverter niche are identified as an infrastructure that could be exploited to somewhat close this gap. Due to potential technical limitations of PV data concentrators, a non-complex VUF approximation formula is tested as a “light” calculation alternative, by comparing it against conventional VUF. The comparison results are obtained from Monte Carlo load flow simulation for an unbalanced LV network.