Optimal charging of plug-in electric vehicles observing power grid constraints

Plug-in electric vehicles (PEVs) impose considerable loads to existing power grids, and consequently, they can challenge power quality and reliability of power systems if their charging is not coordinated. To use existing distribution systems for PEV charging without upgrading them, coordinated charging is inevitable. In this study, an optimal PEV dynamic charging method is proposed observing power grid thermal ratings and voltage quality. The problem is formulated as a standard non-linear programming with minimising energy losses over the charging span as objective function subject to PEVs and power system security constraints. Node voltages and power losses are explicitly and precisely formulated in the proposed method. Coordinated charging span of PEVs starts from evening, when PEV owners arrive home, to the next day morning, when the owners need their car charged and ready to use. The IEEE 31-bus distribution system in highly stressed conditions is used to evaluate the performance of the proposed method in the worst voltage status. According to obtained results, discussed in detail, voltage quality constraints are more restricting than equipment thermal rating in PEV optimal charging because of mostly radial structure of distribution systems. The results confirm the efficiency of the proposed method.