Electric power system for a Chinese fuel cell city bus

A state-of-the-art Chinese fuel cell city bus, using a hybrid power system is proposed. This comprises a proton exchange membrane fuel cell and Ni/MH batteries to combine the high energy density of fuel cells with the high power density of batteries. A dc/dc converter is placed between the fuel cell and the battery to control the electric power flow. This paper presents a novel control strategy for efficiency of the fuel cell operation and optimization of the hybrid power system for the bus. The control strategy is able to regulate the output current of the fuel cell and the charging current or voltage for the battery while limiting the discharge current of the battery. It can achieve a higher efficiency, longer fuel cell lifetime, and higher drive performance. The hybrid fuel cell power system and the proposed control strategy were verified by using dynamometer and road test experiments. The experimental results demonstrated that the control strategy has great flexibility and generality, and also validated that the peak power capacity of the active hybrid power source and the vehicle drive performance can be significantly enhanced.