Two-stage Electric Vehicle Charging Strategy for Reducing both Charging Cost and Transformer Aging

The increasing charging load of electric vehicles (EVs) will accelerate the aging of distribution transformers. In this paper, a two-stage charging strategy is proposed to alleviate the transformer aging caused by EV charging and reduce the charging cost. In the first stage, an initial charging power curve is obtained by solving an optimization problem, which minimizes the transformer aging during the control period. In the second stage, the charging process of each EV is scheduled considering all the information of connected EVs in the charging station, which minimizes the charging cost along with the penalty for deviation from the initial charging power curve. Simulations have been carried out using the actual charging records of Beijing. The results show the charging processes of EVs can be properly scheduled during the parking time and the goals of reducing charging costs as well as transformer aging can be achieved using the proposed charging strategy.