Widespread use of electric vehicles (EVs) requires investigating impacts of vehicles' charging on power systems. This paper focuses on the design of a new DC fast charging station (DCFCS) for EVs combined with local battery energy storages (BESs). Due to the BESs the DCFCS is able to decouple the peak load demand caused by multiple EVs and decrease the installation costs as well as the connection fees. The charging system is equipped with a bidirectional AC/DC converter, two lithium-ion batteries and a DC/DC converter. The introduction of BES within the DCFCSs is investigated with regards to operational costs of the charging stations as well as the ability of a BES to mitigating negative impacts on the power grid during congestion hours. The proposed solution is shown to reduce not only the installation costs but also the charging time and it facilitates the integration of fast chargers in existing low voltage (LV) grids. A cost-benefit analysis (CBA) is performed to evaluate the financial feasibility of BES within the DCFCSs by considering the installation costs, grid connection costs and battery life cycle costs. E IntroductionINCREASED focus on sustainable transportation and CO2 reduction leads to large investments into electric vehicle (EV) technology from the major car producers. Rising numbers of EVs in major cities and widespread rollout of EV charging infrastructures are introducing new high power loads to distribution system operators (DSOs). In recent years environmental concerns and advances in battery technology drive the rapid development of electrical transportation [1]- [3]. In a sustainable city [4], with an increasing amount of electric vehicles, a lot of concern is raised on EV grid integration as well as a tariff system that allows to control the EVs charging demand [5]- [6]. The EN /IEC 61815 and automotive engineers in U.S. SAE J1772 have proposed the EV charging modes and the maximum current delivered both on alternating and direct current (AC and DC).Currently, the public charging stations in the major European cities are providing 7 -43 kW [7], which with the current EV models and charging stations require more than an hour to cover a range of 150 km.Considering the growing number of EVs over the next 10 years [8], appropriate fast charging infrastructures are anticipated to supply the future EV power demand. Therefore, the widespread use of EVs requires investigating impacts of vehicles' charging on the distribution grids. So far, extensive study has focused on optimizing the EV penetration and the charging infrastructure. An optimal approach is proposed in [9] with a day-ahead energy planning of EVs by scheduling

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-The increasing penetration of Electric Vehicles (EVs) and their charging systems is representing new highpower consumption loads for the distribution system operators (DSOs). To solve the problem of the EV range in terms of driving kilometers, the car manufacturers have invested resources on new EV models by increasing the size of the batteries. To satisfy EV load demand of the new EV models in urban areas the public DC Fast-Charging Station (DCFCS) is indispensable to recharge EVs rapidly. The introduction of the Battery Energy Storage within the DCFCSs is considered in this paper an alternative solution to reduce the operational costs of the charging stations as well as the ability to mitigate negative impacts during the congestion on the power grids. An accurate description of the DCFCS and its design system, which is able to decouple the peak load demand caused by EVs on the main grid and decrease the connection fees. Finally, an economic evaluation is done to evaluate the feasibility and the cost-benefit analysis (CBA) of the DCFCSs. The proposed approach considers various technical and economic issues, such as cost of installation, connection fees and life cycle cost of the batteries. The proposed cost-benefit analysis can be used to verify the effectiveness and applicability of DCFCS in large scale.

Abstract-DC Fast Charging Station (DCFCS) is essential for widespread use of Electric Vehicle (EVs). It can recharge EVs in direct current in a short period of time. In recent years, the increasing penetration of EVs and their charging systems are going through a series of changes. This paper addresses the design of a new DCFCS for EVs coupled with a local Battery Energy Storage (BES). DCFCS is equipped with a bidirectional AC/DC converter for feeding power back to the grid, two lithium batteries and a DC/DC converter. This paper proposes an optimal size of the BES to reduce the negative impacts on the power grid through the application of electrical storage systems within the DC fast charging stations. The proposed solution decreases the charging time and the impact on the low voltage (LV) grid significantly. The charger can be used as a multifunctional grid-utility such as congestion management and load levelling. Finally, an optimal design of the DCFSC has been done to evaluate the feasibility and the operability of the system in different EVs load conditions.

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