Vehicle-Directed Smart Charging Strategies to Mitigate the Effect of Long-Range EV Charging on Distribution Transformer Aging

The recent introduction of affordable long-range electric vehicles (EVs) has the potential to trigger more widespread adoption of EVs with higher charging needs. Increased EV charging can have a detrimental effect on the distribution grid, especially by causing accelerated aging of transformers. Although many EV smart-charging strategies have been proposed to mitigate this problem, centralized and distributed smart-charging strategies require numerous new infrastructure components and, thus, take time and money to implement. This article proposes the term vehicle-directed smart charging to describe strategies that individual EVs can use to charge in a more intelligent way and, thus, lessen grid impact. This article proposes a new vehicle-directed smart charging concept, random-in-window (RIW), which has fixed-rate and variable-rate variants. The RIW strategy allows for random charging start times within a specific time window after the residential peak load has reduced. The RIW strategies are compared to other strategies using the real-world logged driving data from 150 drivers for one week using long- and short-range EV models. A transformer aging model indicates that the RIW strategies are approximately as good as a fully controlled centralized smart-charging algorithm at EV penetration rates up to 60% for long-range EVs and 70% for short-range EVs.