Characterization of charging load for a large number of EV units in distribution grids

Though Electric Vehicle (EV) load has been largely characterized as constant power load, recent research works acknowledge its varying nature concerning voltage. Many research works have experimentally characterized an individual EV load on distribution grids. However, EV load characterization for a large number of EVs has remained mostly ignored. Therefore, this paper characterizes aggregated constant current and constant voltage portions of the combined EV load of a large number of EV units, regarding their combined state of charge (SOC), taking electric vehicle conductive charging standard BS EN 61851-23:2014 as the guidelines. The numerical results based on the characterization show that the aggregated EV load is strongly dependent on the mean and standard deviation of their combined SOC. This paper also compares the differences in the impact of EV charging on The University of Queensland's (UQ) grid assuming the EV loads either follow the developed models or the entire EV load is either constant current or constant power.