Design of Series-parallel Hybrid Electric Propulsion Systems and Application in City Transit Bus

Abstract:- The design approaches and a design case of the series-parallel hybrid electric propulsion system for ground vehicles are presented in this paper. Based on the analysis of the base units and the combination types of the series-parallel propulsion systems, a novel manual transmission is proposed to switch the propulsion system configuration in a low-cost manual-shifted hybrid propulsion system. This propulsion system type has been used in a hybrid transit bus. The sizes of propulsion system components, including engine, electric motors, battery and gear ratios, are designed to satisfy the bus’s drive ability requirements. Moreover, some features, including down-sized engine, idling elimination, regenerative brake, low-speed electric propulsion and proper control strategy, etc., are introduced to improve its fuel economy. The fuel economy of the hybrid bus was evaluated under the city transit bus driving cycle. The result shows that the fuel consumption is on average reduced by 21.3 % of that of the conventional baseline bus under city driving conditions, which identifies the approach’s technical and economical feasibility. Key-Words:- series-parallel, hybrid electric propulsion system, transit bus, design, fuel economy