Evaluating Fast Charging of Electric Vehicles Along Motorways Using Finite Multi-Server Queueing System Simulation

Fast DC charging sites are required along motorways to abrogate the car drivers' anxiety of long-distance travels when driving electric vehicles (EVs) with batteries optimised for efficient average reach. This is important to facilitate the mobility transition to EVs. In this study, a queueing model-based approach to simulate and evaluate fast charging sites equipped with many DC charging points is presented. Charging sites are modelled as multi-server queueing systems with finite waiting space, where the servers represent the charging points and the waiting space the parking area available for EVs waiting for service. To evaluate also arrival and service time distributions that are non-Markovian, the queueing system is evaluated using event based simulation. Exemplary results and a comparison with analogous simulation tools complete the presentation of the simulation approach. On one hand, the simulation reveals the mean potential waiting time per EV before charging can start due to the temporary occupation of all charging points. On the other hand, the tool analyses the aggregated power demand of all charging points. Based on latter, the smart charging mechanism reduces dynamically the individually available charging power if needed to stay below the power grid access limit. This smart charging mechanism causes a small decline in the charging performance at high EV traffic loads when all charging points are maximally occupied. In combination with the state-of-charge depending power demand, the tool provides the user critical insights into realistically expectable waiting times and decreased charging volumes when many EVs charge in parallel. Experimenting with different number of charging points and grid power limitations helps the tool-user, the systems designer, to dimension charging sites along motorways that can efficiently handle future traffic loads