Component sizing and engine optimal operation line analysis for a plug-in hybrid electric transit bus

It is very important to determine the specifications of components included in the drive-train of vehicles at the initial design stage. In this study, a component sizing process and a performance analysis for a plug-in hybrid electric transit bus (PHEB) as a series type hybrid system are discussed based on a certain system configuration and performance targets. Six types of driving cycles and various regeneration ratios (0 to 100%) are considered in order to estimate the battery capacity in an effort to achieve an electric range of at least 20 km when the usable state of charge (SOC) range of the battery pack is limited from 90% to 20% of the total battery capacity. The rating output power of a gen-set (Engine+Generator) is analyzed using a method that sustains the SOC level of the battery in a charge-sustaining mode. The peak power of the engine and gen-set can be determined by considering the output characteristics of the battery pack and the driving motor. Also, this paper presents a definition of an optimal gen-set operating line to minimize fuel consumption at a set level of electric output power. The fuel consumption results are compared to those of a conventional optimal operating line.