Comparative Analysis of Parallel vs Series Hybrid Electric Powertrains

In the United States, more than a quarter of greenhouse gas (GHGs) emissions (27%) are attributed to the transportation sector which comprises mainly of vehicles powered by internal combustion engines (ICE). To reduce the dependence on fossil fuels and the resulting GHG emissions associated with conventional ICE vehicles, plug-in hybrid vehicles are being promoted as a viable near-term vehicle technology. This paper is a comparative experimental study of two types of hybrid systems: parallel (also known as plug-in hybrid) and series (also known as extended-range electric) hybrid systems. The two hybrid systems are modelled on an electric bicycle platform and field tested to analyze their performance. The fuel economy was measured and compared in L/100km and the electric powertrain efficiency of the system was measured and compared in watt-hours per kilometer (Wh/km). A sensitivity analysis is carried out in terms of different transmission gear ratios and the variable setpoints in the hybrid control logic to access the impact these factors have on the performance of the hybrid system. This paper focuses only on the technological aspect of the hybrid system and any social and policy aspects associated are not considered. The constructive modeling of the hybrid system, the limitations faced during the process and the results of the field tests are presented.