Impact of controlling zero sequence current in a three-phase four-wire LV network with PV units

Abstract

The dynamic impacts of controlling zero sequence current in a three-phase four-wire low voltage (LV) distribution network with a four-leg voltage source inverter (VSI) and PV installations are investigated in this paper. The PV VSI is designed to control active power at unity power factor (p.f) with additional neutral and zero sequence current controls. Inherently, most of the three-phase four-wire LV distribution networks exhibit voltage unbalance characteristics due to the connection of single- and three-phase nonlinear loads as well as occurrence of asymmetrical faults in the networks. The control over zero sequence current can improve the inherent voltage unbalance in the LV networks. The transient characteristics of the unbalanced network are investigated utilizing a widely used software environment, PSCAD/EMTDC, for the Energex 11 kV/420 V distribution network in Brisbane, Australia. The performance of the designed four-leg VSI is compared with the traditional three-leg VSI experiencing different asymmetrical faults. The results show that, with the additional degree of freedom from the four-leg VSI, faster fault recovery and lower MVA requirement can be achieved for unbalanced LV networks.