Optimal Sizing and Management of Hybrid Storage System for an Electric Urban Bus Under Real Operating Conditions

This paper focuses on the optimal sizing and management of a hybrid energy storage system for an electric public transportation bus. In this study, the energy flows between the battery pack and the supercapacitor module are managed by employing a strategy, based on the exponentially weighted moving average of the current required by the electric drive. In addition, a multi-objective optimization approach is proposed to define the size of the supercapacitor module and the decay factor of the management strategy, with the pursued objective to enhance the battery pack service life and simultaneously improve the energy utilization of the high-power module. Then, an appropriate power architecture and a PWM control strategy for the DC/DC converter are selected, on the base of the resulting energy flows. In this way, the proposed hybrid storage system, in terms of performance in a real-world operating scenario, is compared with an equivalent battery electric bus. In the end, the results on the hybrid storage system demonstrate a significant reduction in both battery peak power demand and C-rate, contributing to an extended battery lifespan.