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With the popularization of electric vehicles (EVs), the influence on power systems is receiving increasing attention. According to statistics, EVs are in a parking state for more than 90% of the time, thus, the electric energy of the EVs accumulated by aggregators can be used to support the operation of power systems. This paper takes reducing operation costs as the objective function and considers the constraints of EVs and power systems to establish the optimal charging/discharging control of electric vehicles, which meet the operational safety of power systems and convenient driving. The influence on operation costs, peak load, and loss for the proposed charging/discharging two-way control, charging-only control, and free charging modes of EVs are compared. The influence of battery charging and discharging efficiency on these results is also discussed in this paper. Index Terms-Electric vehicle (EV), operation cost, optimal charging/discharging control.Rong-Ceng Leou (M'13) received the Ph.D. degree from National Sun Yat-Sen University, Kaohsiung, Taiwan.Currently, he is with Department of Electrical Engineering, Cheng-Shiu University, Kaohsiung, Taiwan. His research interest are transmission and distribution system planning.

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Abstract:The battery capacity of electric buses (EB) used for public transportation is greater than that of electric cars, and the charging power is also several times greater than that used in electric cars; this can result in high energy consumption and negatively impact power distribution networks. This paper proposes a framework to determine the optimal contracted power capacity and charging schedule of an EB charging station in such a way that energy costs can be reduced. A mathematical model of controlled charging, which includes the capacity and energy charges of the station, was developed to minimize costs. The constraints of the model include the charging characteristics of an EB and the operational guidelines of the bus company. A practical EB charging station was used to verify the proposed model. The financial viability of this EB charging station is also studied in this paper. The economic analysis model for this charging station considers investment and operational costs, and the operational revenue. Sensitivity analyses with respect to some key parameters are also performed in this paper. Based on actual operational routes and EB charging schemes, test results indicate that the EB charging station investment is feasible, and the planning model proposed can be used to determine optimal station power capacity and minimize energy costs.