Study On Hybrid Power System Of PHEV City Bus

To solve the problems of energy crisis and environmental pollution which modern socity are faced with, new energy vehicle is considered to be an effective roadmap. Nowdays, different forms of new energy vehicles, especially PHEV(Plug-in hybrid electric vehicle), have been extensively studied at home and abroad. PHEV possesses the advantages of traditional internal combustion engine vehicles and pure electric vehicles, being currently feasible to solve the energy and environmental issues due to outstanding market performances.Whereas, for PHEV, the charge and discharge current rate is much bigger, more often reaches upper and lower limit of SOC compared with EV and HEV. Especially for plug-in hybrid electric city bus, improving the proportion of feedback braking is of vital significance. In this paper, matching of hybrid power system, development of power management system, power allocation strategy design of hybrid power system for plug-in hybrid electric city bus are studied.By analyzing the functions which the hybrid power management system is equipped with, the topology of the hybrid power management system is selected. The main contributions of the paper include the hardware and software designings of PCU, PCM and bi-directional DC-DC converter, what is more, the whole system of hybrid power management designed meet the requirements of functions.The equivalent circuit models of lithium battery and Ultracapacitor were constructed through parameter identification experiment. In consideration of the effects of SOH on the battery model and the influencing factor of SOH, the SOH estimation model of lithium battery was established, meanwhile, the battery model was modified by means of SOH. Afterwards, the efficiency model of the DC-DC converter was built on the basis of efficiency experiments. In the end, the high accuracy model of the hybrid power system in whole life cycle was developed by Simulink. On this basis, this paper presented a power allocation strategy for hybrid power system based on logic threshold values in order to improve vehicle economy and battery life, achieving the purpose of designing hybrid power system. In terms of strategy, logical threshold of important parameters which largely affected the vehicle economy and battery life got offline through PSO algorithm. Compared with the hybrid power system and single battery simulation system, battery life and vehicle economy could be improved obviously under the hybrid power system.Finally, the hybrid power management system was applied for traditional hybrid system bench for purpose of monitoring battery system、verifying power management system、testing current and the estimation accuracy of SOC. Power allocation strategy for hybrid power system was verified with a small hybrid power system. The experimental results showed that the power allocation strategy applied in the hybrid power system worked well, which obviously improved battery life and vehicle economy, furthermore, be a better solution for the issues about current shock and efficiency of PHEV batteries...