Load characteristics of electric vehicles in charging and discharging states and impacts on distribution systems

With incentive policies introduced in developed countries and advent of electric vehicle (EV) technologies, especially the development of high energy and power density batteries, the penetration level of EVs is expected to grow rapidly. A high penetration level of EVs could bring about a large impact on power grid, particularly on distribution systems. This paper is to investigate such an impact and countermeasures. The Monte Carlo simulation method is first utilized to study the charging load in the uncoordinated charging mode and the discharging capacity curve in the vehicle-to-grid (V2G) mode. The EVs´ impacts in terms of system loads, power losses and voltage deviations are then analyzed in both the uncoordinated charging mode and the V2G mode. The PG&E 69-node distribution system is employed in the case study. Simulation results have shown that uncoordinated charging at a high EV penetration level will cause a negative impact in all the aspects analyzed. By reasonable management of EV charging/discharging, however, the adverse impact could be significantly alleviated to ensure secure and economic operation of the distribution system.