Optimal Operation with Robo-chargers in Plug-in Electric Vehicle Charging Stations

Plug-in electric vehicles have seen unprecedented market growth, while charging facility infrastructure is falling behind. Worse still, these limited charging resources are being utilized quite uneconomically - commonly occupied by fully-charged PEVs for a long time, known as overstay. In this paper, we propose a charging facility and operation innovation to tackle this challenge. We introduce the idea of Robo-chargers, an automated charger that can proactively rotate among PEVs for charging service. We develop an operation model for management in a mixed-type charger charging station, equipped with both Fixed-chargers and Robo-chargers. The model incorporates the combinatorial nature of vehicle-charger assignments, charging dynamics, and customer waiting behavior in order to maximize the station's revenue. We further reformulate the model as a mixed-integer linear programming problem. In numerical studies based on real-world data, we find that incorporating Robo-chargers into a charging station is profitable when heavy overstay occurs, justifying the increased capital cost. For a given budget, a mix of Fixed-chargers and Robo-chargers can achieve the best operation performance by balancing robo-charger flexibility, cost, and total charging points.