Series and Parallel Hybrid System Performance Comparison Based on the City bus Cycle

In this paper, a series and a parallel hybrid system working characteristics are compared and analyzed based on city bus cycle testing to present the advantages and disadvantages. Two city buses in different hybrid types called WG6120HD and EQ6110HEV have bee put into operation on the city bus route in Wuhan. There are two architectures are proposed in the paper. The hybrid system components working properties come up according to the practical bus route testing data analysis. In terms of the series hybrid system, the engine independent working and effective regenerative braking system configuration are significant to improve the system global efficiency. The system efficiency is determined by the battery efficiency losses as well. Special attention is located on engine efficiency difference between the stable and the dynamic working conditions in a series hybrid system. The motor auxiliary drive allows a reduction of fuel consumption for the parallel hybrid system, on the other hand, the motor assistance introduces the negative effect of the incurred three times efficiency losses to the system. The influence caused by the engine wide dynamic fluctuation on the efficiency is stated as well.