Off-vehicle Energy Store Selection for High Rate EV Charging Station

Abstract

Fast Electric Vehicle (EV) charging, defined as a charging power greater than 120kW, is needed to help overcome range anxiety, the worry of an EV owner that an EV battery will run out of energy before a destination is reached. Fast charging stations require a high power grid connection, which limits the available installation locations and increases grid connection costs. A stationary off-vehicle energy store can be used at a fast charging station to buffer the power between the grid and the EV to minimise and control the grid connection power. It is shown that for a charging station in the near future, which is used infrequently, a small (-50kWh) offvehicle energy store that can accept high C-Rates (1-10C) during charge and discharge may be used. It is suggested that lithium iron phosphate batteries are used for this purpose and experiments are currently being undertaken to validate this. For a charging station further in the future, which is used more frequently, a much larger (4MWh) off-vehicle energy store with lower C-Rates (<1C) is required. It is suggested that lead-acid batteries or flow batteries are used for this purpose. If flow batteries are chosen, supercapacitors or lithium-ion batteries could be used in a hybrid system to deal with power fluctuations that occur as different numbers of EVs arrive to charge.