Control strategies for electric vehicle (EV) charging using renewables and local storage

Abstract

The increase of electric vehicle (EV) and plug-in hybrid-electric vehicle (PHEV) adoption creates a need for more EV supply equipment (EVSE) infrastructure (i.e., EV chargers). The impact of EVSE installations could be significant due to limitations in the electric grid and potential demand charges for residential and commercial customers. The use of renewables (e.g., solar) and local storage (e.g., battery bank) can mitigate loads caused by EVSE on the electric grid. This would eliminate costly upgrades needed by utilities and decrease demand charges for consumers. This paper aims to explore control systems that mitigate the impact of EVSE on the electric grid using solar energy and battery banks. Three control systems are investigated and compared in this study. The first control system discharges the battery bank at a constant rate during specific times of the day based on historical data. The second discharges the battery bank based on the number of EVs charging (linear) and the amount of solar energy being generated. The third discharges the battery bank based on a sigmoid function (non-linear) in response to the number of EVs charging, and also takes into consideration the amount of renewables being generated. The first and second control systems recharge the battery bank at night when demand is lowest. The third recharges the battery bank at night and during times of the day when there is an excess of solar. Experiments are conducted using data from a private site that has 25 solar-assisted charging stations at Oak Ridge National Laboratory (ORNL) in Oak Ridge, TN and 4 at a public site in Nashville, TN. Results indicate the third control system having better performance, negating up to 71% of EVSE load, compared with the second control system (up to 61%) and the first control system (up to 58%).