Thermal Management Simulation Of Fuel Cell-Lithium Battery Hybrid System Based On NEDC Operating Conditions

With the increasingly serious problems of environmental pollution and sustainable utilization of energy,new energy vehicles have gradually stepped onto the stage of history.However,new energy vehicles powered by lithium batteries were limited by endurance and their service life,which cannot reach the level of internal combustion engines.The new energy vehicles powered by fuel cells（FC）have the advantages of long life and "zero emission".Therefore,FC vehicles have become a new trend of new energy vehicles and had broad prospects.However,fuel cells still exhibit some problems,such as low efficiency and difficult start-up at low temperatures.In this paper,the energy management of fuel cell-lithium battery hybrid power system was studied and the strategy of the heat management system of the electric-electric hybrid power system was designed.MATLAB/Simulink was used to model and simulate the heat management system.This paper tried to solve the problems of the difficult start-up of the electric-electric hybrid power system at low temperature and effectively improved the efficiency of the fuel cell-lithium battery hybrid power system.First,the performance of Proton exchange membrane fuel cell（PEMFC）stack was experimentally tested to analyze the effects of temperature,excess hydrogen coefficient,and excess air coefficient on the output performance of PEMFC stack.The results showed that the efficiency of PEMFC stack increased with the increasing temperature within 50℃.The output performance of PEMFC stack was gradually improved but efficiency was decreased with the increasing excess hydrogen coefficient.At low current density,the increasing excess air coefficient had little effect on the output performance of PEMFC stack but improved the output performance at high current density.In addition,the performance of lithium batteries was studied in a constant temperature and humidity box and lithium battery charging and discharging cabinet.It was concluded that the outperformance of lithium batteries increased with the increasing temperature within 25℃ and the discharge performance of lithium batteries improved with the lower discharge rate when the charge state（SOC）of lithium batteries was certain.Then,based on the experimental data of PEMFC stack and lithium battery,MATLAB/Simulink was used to simulated and analyzed an electric-electric hybrid system based on hierarchical energy management strategy and minimum hydrogen consumption energy management strategy.The results showed that both strategies fulfilled the power demand of the hybrid system.The hydrogen consumption of the hybrid system under the hierarchical energy management strategy was less than that of the strategy of hierarchical energy management.Finally,based on the energy management strategy and the experimental data of PEMFC stack and lithium battery,a set of the heat management plan was made and simulated by MATLAB/Simulink.It was concluded that the hydrogen consumption of the hybrid system based on the two energy management strategies was reduced when heat management was carried out.The hybrid power system adopted the hierarchical energy management strategy was greatly influenced by the SOC of lithium batteries.When the SOC of lithium battery was high,heat management strategy had a great effect on the hybrid power system.The hydrogen consumption of the hybrid power system based on the energy management strategy of minimum hydrogen consumption decreases relatively little after the increase of heat management.