The effect of high penetration level of distributed generation sources on voltage stability analysis in unbalanced distribution systems considering load model

Static voltage stability is considered as one of the main issues for primary identification before voltage collapsing in distribution systems. Although, the optimum siting of distributed generation resources in distribution electricity network can play a significant role in voltage stability improving and losses reduction, the high penetration level of them can lead to reduction in the improvement of load-ability. Moreover, the rapid variation and types of loads in distribution networks will have a significant impact on the maximum load-ability across the whole system. In this paper, a modified voltage stability index is presented with regard to distributed generation units (DG) along with two-tier load model. By applying the Imperialist Competition Algorithm (ICA), the best size of DG with corresponding of DG placement is used to improve the voltage stability and reducing the losses. It is shown in the paper that the DG penetration level can have influence on load-ability of the system and also the voltage regulators performance. The simulation results on the standard IEEE-13 Bus test feeder illustrate the precision of studies method and the load-ability limits in the system, taking into account the high penetration level of distributed generation units.