Abstract: Voltage instability problems have become important issues in unbalanced multiphase distribution networks. This paper expands the well-known voltage index V/V0 and defines an improved positive sequence voltage index of Vcollapse/Vno-load to identify the weakest single-, two- and three-phase buses in unbalanced multiphase distribution networks. First, the ranking index is validated based on grid losses and PV curves without and with compensation devices. Then, the index is utilized to place single-phase shunt capacitors, three-phase DG without and with SVC devices at the most appropriate buses of the IEEE unbalanced multiphase 13 node test feeder using the MATLAB/SIMULINK software. Finally, simulation results are presented to show the application of the proposed approach in improving voltage stability under unbalanced loading and/or network conditions.

Keywords: Voltage stability, weakest bus and unbalanced distribution network.