Optimal on-board energy buffer design for fuel-cell hybrid intercity vehicles

A long-distance or intercity bus has been the primary transport mode for people travelling across a country. Technological shift to the next-generation of electric vehicles marks a significant departure for traditional automakers and hence leads to develop zero-emission buses and utilising fuel cells (FC) is one of the potential alternatives. This paper proposes the optimal calculation of the energy storage in an FC hybrid intercity bus using either batteries or supercapacitors (SCs) as the main energy buffer. The long-distance driving cycle used is modified from the Highway Fuel Economy Driving Schedule and the mixed-integer PSO method is adopted. The design objective is to minimise the cost of the energy storage and FC, and hydrogen consumption of the total route. The results show and compare the optimal energy storage and FC sizing between the FC-battery and FC-SC buses. The FC-battery bus is cost-effective, and the battery capacity is also sufficient to supply all auxiliary loads during FC start-up. However, frequent charge and discharge cycles could shorten the battery's lifetime. From a hydrogen consumption viewpoint, the FC-SC bus is slightly more efficient because the FC always operates at a higher efficiency region, and it takes a shorter time to recharge the SC.