Voltage Regulation Under Unbalanced Power Flow in Active Four-Wire Low Voltage Distribution Grids

The increasing penetration of distributed energy resources in Low Voltage Distribution Grids (LVDGs) has a severe impact on the grid’s voltage profile. In active LVDGs the controllable assets are mainly single-phase inverters which most often they are unevenly distributed amongst the supply phases. The majority of voltage support schemes in the literature assume that the phases are decoupled and utilize the single-phase inverters in per-phase regulation methods. However, the particularities of LVDGs, namely the inductive coupling from the distribution lines and the neutral coupling from the fourth wire, can result to a strong phase coupling. Consequently, conventional voltage support schemes by single-phase inverters in active LVDGs can cause unbalanced power deviations in one phase and due to the phase coupling it can have a significant impact on the voltage of a different phase. In this paper, the phase coupling, its impact on voltage regulation, and the factors that contribute to its intensity are analysed. In addition, it is demonstrated how two traditional voltage regulation schemes become ineffective due to the phase coupling. Finally, a reactive power compensation scheme is presented that exploits the mutual voltage deviations induced by the phase couplings in order to improve the voltage regulation capabilities in LVDGs.