A Novel Fairness-Based Cost Model for Adopting Smart Charging at Fast Charging Stations

Abstract

This research introduces a cost model for application at fast charging stations (FCSs) with the aim to adopt smart charging, which can mitigate voltage fluctuation caused by the on/off status of FCS. When the operation of FCSs causes a voltage fluctuation and light flicker, the FCSs may be disconnected, as per the utility general standard practice, which results in financial loss represented by FCS downtime. However, FCS downtime can be avoided by applying the smart charging method referred to in this paper, or by installing mitigation devices that are available on the market. The proposed smart charging method provides three charging powers (or options), namely premium, regular, and economic, which consumers can select according to their needs and/or priority, whether this may be time or cost. Thus, the output power of each type is different as well as the per unit cost. The offered cost of smart charging is reliant on a ‘fairness’ policy that is, from the viewpoint of an FCS operator or investor, characterized by the value of cost for any customer at the FCS being equivalent to the customer’s value of time. For instance, customers A and B require X kwh from the FCS. When arriving at the FCS, if customer A values time the most, the premium power can be selected with the highest $/kwh cost. If the cost is more valuable to customer B, regular or economic power can be selected, but customer B will spend more time than customer A to get the same X kwh. The proposed fairness policy indicates that, to get the required X kwh, the percent of total costs saved by B (by using regular or economic power) in comparison to A is equivalent to the percent of total time saved by A (by using premium power) in comparison to B, for the same X kwh. The annual cost of applying smart charging at the FCS is estimated and compared with the annual cost of the best flicker mitigation device. The comparison reveals that distribution static compensators are considered the cheapest mitigation device, according to the cost per kVAr basis and the total annual equivalent cost. The proposed smart charging method achieves a tremendous reduction in the cost of mitigating the voltage fluctuation and light flicker. The annual cost of the proposed smart charging method is less than the annual cost of distribution static compensators by a minimum of 90% to a maximum of 99%.