Joint optimization of vehicle scheduling and charging strategies for electric buses to reduce battery degradation

Abstract

The widespread adoption of electric buses (EB) is hampered by battery degradation. Battery degradation refers to the phenomenon of lithium batteries shrinking in capacity and eventually becoming unusable due to the extensive charging and discharging behavior. This paper proposes a joint optimization of EBs vehicle scheduling and charging strategies that considers both explicit charging cost and implicit battery degradation cost. First, we construct a mathematical optimization model through the graph theory. Then, the battery degradation cost is computed by investigating the relationship between battery degradation and state of charge (SoC) during charging/discharging. Finally, the proposed model is linearized and solved efficiently. Numerical results show that 7.45% of the battery degradation cost and 6% of the total cost can be saved just by simply adjusting the vehicle scheduling and charging strategies. The battery degradation cost is much larger than the charging cost, which emphasizes the need to consider battery degradation. The results also provide some practical suggestions for operators. The lowest possible initial SoC can reduce battery degradation, while increasing the number of buses has little impact.