Sizing optimization research considering mass effect of hybrid energy storage system in electric vehicles

Abstract

This paper uses dynamic programming to deal with the sizing optimization problem for battery/ ultracapacitor hybrid energy storage systems in electric vehicles to minimize the electricity cost and battery degradation cost. The sizing of the battery pack is designed to meet the minimum mileage of electric vehicles. The optimal sizing of the ultracapacitor pack is optimized by dynamic programming, especially considering the influence of ultracapacitor mass on the load power. Results show that the operation cost firstly decreases rapidly as the ultracapacitor number increases. After a turning point, the operation cost slowly increases due to the increasingly heavy ultracapacitors, thus the turning point is chosen as the optimal sizing result. Two different optimal sizing schemes for designing different vehicle types are proposed through results fusion under low, medium, and high-speed driving conditions. Compared with sizing optimization results without load power changes due to ultracapacitor mass, the proposed optimal schemes add more ultracapacitor packs and can therefore reduce the vehicle operation cost by 3.94% to 6.54% under different driving conditions.