Application of distributed generation (DG) units in distribution networks has increased
in recent years. Sizing and sitting of DG units are two important factors which should be
considered, especially for reduction of power losses in distribution system. This paper presents a
new approach for DG placement in distribution systems using the mixed integer nonlinear
programming (MINLP). This approach determines the optimal number, sitting and sizing of DG
units in both radial and meshed distribution networks with the objectives of reducing the power
losses, as well as minimizing the investment and operation costs of DG units, and the monetary
value of voltage stability index improvement. The performance of the proposed method is
compared with the genetic algorithm (GA), particle swarm optimization (PSO), combined GA and
PSO, and combined loss sensitivity factor and simulated annealing (LSFSA). Compared with the
conventional methods, the proposed scheme can be applied in the meshed distribution networks as
well. A 33-bus radial network and CIVANLAR meshed distribution system have been used for
simulation studies. The obtained results approve the efficiency of proposed method for sitting and
sizing of DG units in distribution networks.