A two-stage method for optimal placement of distributed generation units and capacitors in distribution systems

[Display omitted] •A two-stage method is applied for solving the DGs and capacitors placement problem.•Two VSFs based on VD and VSI are used to reduce the search space.•The CBA is used to find the optimal locations and sizes of DGs and capacitors.•The CBA is used to optimize single and multi-objective functions.•The proposed CBA is applied to small and large-scale systems to show its robustness. This paper proposes a two-stage procedure to enhance the distribution system performance by determining the optimal sizes and locations of distributed generations (DGs) and capacitors considering single and multi-objective functions. In stage-1, two voltage sensitivity factors (VSFs) based on voltage deviation (VD), and voltage stability index (VSI) are proposed to reduce the search space (SS) by selecting the candidate buses for DGs and capacitors placement. In stage-2, the chaotic bat algorithm (CBA) is applied to find the optimal sizes and locations of DGs and capacitors, according to different objective functions (OFs) and system constraints. The considered OFs are real power loss reduction, total VD minimization, and total VSI maximization. The multi-OF, which aims to optimize these objectives simultaneously, is also considered. The load flow calculations are carried out using the backward/forward sweep (BFS) algorithm. The proposed methodology is evaluated and tested on small and large-scale standard test systems, namely 34-bus and 118-bus radial distribution systems, through different case studies. The numerical results obtained by the proposed procedure are compared with other methods in the literature to show the superiority of the proposed procedure for reducing the total real power loss and improving the voltage profile, especially at increasing the power system sizing.