An Investigation of Opportunity Charging with Hybrid Energy Storage System on Electric Bus with Two-Speed Transmission

As one of the most popular and important forms of massive transit, the public bus contributes to a healthier environment compared to private vehicles. Through the electrification of the public bus, energy consumption, carbon emission, and air pollution can be significantly reduced. However, the limited driving range and high battery replacement cost put significant barriers to its large-scale commercialization. Thanks to the development of wireless charging technology and opportunity charging strategy, the driving range can be improved. However, the battery has to suffer additional impulse current generated by opportunity wireless charging. In this paper, a hybrid energy storage system (HESS) that combines battery and supercapacitor and related energy control strategy is proposed to smoothen the impulse current and extend the battery lifespan. A comprehensive investigation of the combined impacts of the opportunity charging and HESS is carried out in terms of driving range extension and battery lifespan improvement. The detailed HESS model and powertrain model are built. A global optimizing method, dynamic programming, is adopted as the energy management strategy under the Chinese heavy-duty commercial vehicle test cycle-bus (CHTC-B). A battery degradation model is employed to evaluate its health with 60 kW wireless charging. The results demonstrate that the proposed energy control strategy for HESS could improve battery health and extend bus driving range concurrently via opportunity charging.