Fuzzy-Based Control for Charging of Medium- and Heavy-Duty Electric Vehicles with Vehicle-to-Grid Capabilities

The electrification of vehicles and the charging required to operate them has applied strain on the distribution networks. High loads and current flows arising from fast charging with power output in the hundreds of kilowatts lead to power quality concerns such as voltage sags, and greater substation loading. These concerns are expected to worsen as the heavy-duty vehicles become electrified and higher charging rates are introduced, potentially up to megawatt-scale charging.Controlled charging can be employed to mitigate the issues presented by vehicle charging while meeting the needs of the owner. These strategies smooth out the load curve by reducing maximum charging rate across the predicted plug-in time. Charging loads are also reduced during periods of high load to reduce overall strain on the grid. Stress can be further reduced by injecting power into the grid during these periods to assist power generation through vehicle-to-grid operations.This paper proposes a fuzzy-based control strategy to vary the charging rate of medium- and heavy-duty vehicles such that charging is reduced during times of high load and voltage sag if the vehicle state-of-charging and remaining plug-in time are high. If the opposite occurs then the charging rate is increased. Vehicle-to-grid capabilities are incorporated into the fuzzy logic controller through the introduction of a negative charging rate membership function. This allows for discharging of the battery if sufficiently charged during periods of high load. The proposed strategy is tested in MATLAB and OpenDSS on a charging station with 250 kW chargers in a distribution network based on an industrial Australian town. Two hosting capacity indices based on substation loading and voltage deviation are used to quantify the number of chargers that can be supported. The fuzzy logic control reduced voltage sag at the feeder ends while increasing the hosting capacity of the distribution network.