Energy management and ECO-strategies modeling of electric bus fleets in Barcelona city

Abstract

The paper studies the development of ECO-strategies, including ECO-driving, ECO-charging, and ECO-comfort, for fleets of electric buses traveling in two routes in Barcelona, route H16 and route L33, in terms of their energy utilization, total cost of ownership and the impact on the grid. The efficacy of each ECO-strategy is evaluated with respect to the driving and climatic conditions. To evaluate the effects of climate, fleet simulations for Barcelona are run for mid-summer and mid-winter, in normal mode as well as for each of the ECO modes independently and all combined. To evaluate the effects of driving condition, two different routes with different average velocities and elevation profiles are considered. The fleet consists of four types of electric buses that are evaluated, including two 12m and two 18m buses, with different battery capacities and chemistries. Simulation results showed that the battery capacities for the 12m buses were more than sufficient to allow the buses to undertake two or three return trips before requiring charging. However, for the 18m buses the capacity was just sufficient to make one return trip in either of the routes being considered, not allowing much room for battery capacity degradation; thus, it is recommended to apply ECO-features to reduce the energy utilization rate, increase the number of charging points along the route, or increase the battery capacity. Results show that ECO-driving is more effective when the average velocity of the route is higher; thus, route H16 with an average route velocity of 2.64m/s shows no discernable energy savings, while route L33 with an average route velocity of 3.23m/s has 5% ~ 7% energy savings. Similarly, results show that ECO-comfort is optimized for cooling, with substantial energy savings of 23% during summer and 18% during winter. Finally, ECO-charging shows more energy savings for high charging c-rate; LTO batteries, with a c-rate of -5C showing 5% ~ 6% more savings than NMC battery, with a c-rate of -2.5C.