Nowadays, with the increasing growth of non-linear loads and plug-in hybrid electric vehicles charging stations in the distribution system and the commitment of distribution companies to provide loads of consumers, system planning and development with the closest state to standard conditions is very important. In this paper, the problem of the design and development of distribution systems with the aim of minimizing system investment and operation of the system in the presence of nonlinear loads is discussed. This problem has been proposed in an optimization model to improve and maintain power quality standards, including improved harmonic conditions and improved system voltage drop in critical conditions. These critical conditions have a major impact on sensitive loads.