Abstract — This paper deals with the design of a grid- friendly ultrafast electric vehicle charging demonstrator. High charging power and short charging times impose peaks to an electricity distribution system, which necessitate over-dimensioning of the grid connection. A mitigation option lies in partial decoupling the load from the grid, achieved with the application of energy storage elements. A calculation methodology for energy storage elements is proposed and their interconnection possibilities to an ultrafast EV charging spot discussed. Index Terms — electric vehicles, energy storage, ultrafast charging. I.  INTRODUCTION An inherent obstacle before a major breakthrough to the market of the electric vehicles (EV) has set itself inside the onboard traction energy storage, limiting the vehicle’s autonomy and autonomy flowrate. The latter term refers in this paper to the distance gained per minute of recharging. To emphasize the situation, a comparison between a small fuel efficient family car and its electric counterpart is drawn in Table I. TABLE I. A COMPARISON BETWEEN DIESEL AND ELECTRIC VEHICLES Parameter Diesel car Electric vehicle Consumption 5 l / 100 km 15 kW•h / 100 km Tank capacity 45 l 24 kW•h Autonomy 900 km 160 km Tanking speed 35 l/min 50 kW Autonomy flowrate 700 km/min 4 km/min The comparison in Table I allows concluding preliminarily that one liter of diesel fuel equals around 3 kW·h of tank-to-wheel (TTW) electrical energy. Actually, the onboard battery supplies not only traction power, but also heating, cruise control, air conditioning and other auxiliaries, which result in an additional load of up to 30 % [1]. Simple calculations show, that an EV should have a battery capacity of 135 kW·h and charging power of 6.3 MW to match the autonomy and autonomy flowrate of an equivalent diesel car. With the actual and tangible energy storage technologies as well as with power system limitations, these values are not reachable. However, reaching the autonomy values should not be a final objective, as no driver under normal conditions would cover 900 km without any intermediate stops. The recent studies on drivers’ habits demonstrate, that a daily distance for 80 % of all cases does not exceed 50 km, which makes conventional slow (6 h…8 h) recharging in  This work was supported by the Competence Centre Energy and Mobility (CCEM) and Swisselectric Research domestic conditions possible [2]. For those, whose trips exceed the EV autonomy, long charging times even with the available “quick” chargers resulting in prolonged travel times make the all-electric vehicles unattractive. Thus, to make more ground for the electromobility, charging times must be shortened in order to compete with the average speed of a thermally powered car. The objective charging time 5 minutes, aimed by the authors, brings along additional requirements to the hardware. Whereas a limited demonstrator is discussed here, an ampler deployment of ultrafast charging issues at higher EV market penetration has been studied based on statistical analysis [3]. II. STATE OF THE ART Internationally, the requirements on fast charging installations are defined by IEC 61851-23, setting the standards for dc charging from an external charger [4]. One of its implementations is the CHAdeMO method, approved by several vehicle manufacturers [5], [6]. With CHAdeMO, the charging time is externally limited by the allowable current and voltage of the connector, 125 A and 500 V, respectively. Thus, an average EV needs 20 to 30 minutes for recharging from zero to 80 % of its rated capacity. This maximum state of charge (SoC) value at high charging rates is caused by utilizing only the constant current part of the battery charging curve (Fig. 1), where the charging is interrupted at the terminal voltage cutoff level in order not to damage the battery. The remaining 20 % can be delivered at constant voltage; this process has, however, an asymptotic character. t SoC u i i = const u = const t 1 t 2 u, i, SoC SoC 80 % Fig. 1. A typical battery charging curve [7] As the main objective of ultrafast charging is to remarkably shorten the recharging time t ch in comparison to the actual driving time t dr , their values must be expressed first. The driving time t dr,i from charging spot i-1 to charging spot i depends on the rated battery capacity E EV expressed in kW·h, energy consumption at given speed An Ultrafast EV Charging Station Demonstrator H. Hõimoja * , A. Rufer * , G. Dziechciaruk ** , and A. Vezzini ** * Laboratoire d’électronique industrielle, EPFL-STI-LEI, Station 11, 1015 Lausanne (Switzerland) ** Labor der Industrieelektronik, BFH-TI-LIE, Quellgasse 21, 2501 Biel (Switzerland) 978-1-4673-1301-8/12/$31.00 ©2012 IEEE 2012 International Symposium on Power Electronics, Electrical Drives, Automation and Motion 1390