Impact of EV battery chargers on the power quality of distribution systems

A summary of the actual state of battery charger harmonics is presented. The effect of harmonic distortion on the distribution system, especially on distribution transformers, is analyzed. A program was developed, which allows the consideration of the transformer life consumption as function of the battery charger characteristics and charging algorithm. The program is considered a distribution planning and management tool. The proposed tool can be easily applied to determine the optimum charging time as function of the existing load, ambient temperature, and time of day. From the study, it can be deduced that direct connect-and-charge scheme can be detrimental to the transformer life, especially under high temperature and large load. Calculations show the existence of a quadratic relationship between the transformer life consumption and the total harmonic distortion (THD) of the battery charger current. Furthermore, the current THD should be limited to 25-30% in order to have a reasonable transformer life expectancy.