Optimal allocation and sizing of DG units considering voltage stability, losses and load variations

•DG allocation with a new index for voltage stability and power losses.•A long-term scheduling for optimal allocation and sizing of DG unit.•A general equation of generation for different loading condition.•DG allocation problem is solved using ICA and verified by CSA.•The DNOs generation scheduling has been facilitated over the planning horizon.

This paper proposes a new index to determine the optimal size and location of DG units, in order to minimize active power losses and enhance voltage stability margin considering load variations. A modified form of Imperialistic Competitive Algorithm (ICA) method is used to solve the optimization problem. To provide a comprehensive perspective for network scheduling, the load variations are considered. The load linear changes are from 50% to 150% of the base load (in 1% steps). At each step, the optimal size and location of the DG unit are determined and then, general expressions for DG sizes as a function of load level are concluded through curve fitting technique. These general expressions can be used as a suitable tool for network planning.The proposed method is applied to 34-bus and 69-bus test systems and the results are compared with the results obtained from cuckoo search algorithm in order to validate the proposed methodology.