Optimal planning of heterogeneous charging stations: a methodological framework for simultaneous siting and sizing under finite queue constraints

Scalable deployment of electric vehicle (EV) infrastructure necessitates balancing capital investment, grid constraints, and service quality. Conventional planning models frequently assume homogeneous charging equipment and infinite queuing capacities, yielding unrealistic configurations for dense urban environments. This study addresses these limitations by developing an integrated macroscopic optimization framework that synthesizes metaheuristic optimization with analytical finite-capacity queuing theory. The framework simultaneously resolves station siting and internal heterogeneous sizing based on localized EV behavioral and technical parameters. It minimizes total daily system costs by incorporating travel time and queuing delay penalties, while mitigating the computational complexity inherent to large-scale urban network optimization. The model is validated by comparing the economic and operational performance of hybrid- versus single-type station networks using synthetic data from the Tama Area, Tokyo. Results indicate that heterogeneous configurations reduce total daily system costs by approximately 42% compared to fast-charger-only networks and 21% compared to medium-charger-only networks, reducing total social expenditure to approximately ¥2.6 million per day. The optimization reveals a structural preference for distributing fast-charging assets to maximize spatial coverage rather than concentrating capacity within central hubs. Sensitivity analysis demonstrates that the framework actively adjusts traffic routing to accommodate varying peak demand durations, managing the trade-off between localized queuing and extended travel distances. Furthermore, limit-state stress analysis indicates network resilience, maintaining acceptable service levels under substantial peak demand surges. This framework provides a robust data-driven decision support tool to configure EV charging stations in alignment with the economic and physical realities of modern cities.