Study On Dynamic Characteristic Of Pem Fuel Cell Systems For Vehicle

Proton exchange membrane fuel cell(PEMFC) has become the major type of fuel cells research for its high-energy efficiency ,pollution-free characteristics and low operation temperature. Proton exchange membrane fuel cell is the most probable for automobile bus, electrical equipment, portable power and stationary product, and it has a very good foreground. Author studied PEM Fuel Cells by establishing models for work parameters optimization and by Computer Fluid Dynamic (CFD) analysis on specific Fuel Cell model. The study aims at improving work performances of PEM Fuel Cells. The author described the study of the dynamic characteristic with two ways, based on distributed-parameter model and lumped-parameter model.Without regard to the time lag of air supply system, an electrochemical model of PEM Fuel Cells and a stack model under steady condition were established with Matlab software. PEMFC output performances influenced by working parameters (esp. working pressure of reactants and stack temperature) were simulated using Matlab software. It is concluded that PEM Fuel Cells'performances can be evidently improved by increasing work temperature and work pressure. Fuel cell power increases 6.09% with every 20K interval of temperature increase, while the amplitude descends slightly under high temperature condition.Regarding to the time lag of air supply system software MATLAB / SIMULINK were utilized to create the simulation model of fuel cell dynamic output performance as power level changes. Power output response as power level changes from 50kW to 30kW. air supply system contributes an evident impact on the fuel cell stack dynamic behavior. In order to keep stack parameters output in steady state, air pressure inequality for a given compressor is advised to be less than 2%.The proton exchange membranes have their own optimum range of work temperature. This is because the heat stability of PEM and proton conductibility will descend badly when the temperature exceeds a specific point. The influence of current density and gas humidification on fuel cell performance and membrane temperature distribution are discussed. The results are as follows: The membrane temperature under flow channel is higher than under shoulder and the more current density produced, the greater the current density and the membrane temperature produced; the current density and membrane temperature changes with the change of gas humidification. Under the same conditions, gas humidification in the anode is more efficiency than in the cathode to improve PEMFC performance and the degree of membrane wetting in low humidity conditions. Based on computer simulation , the primary research of this thesis concentrates on the internal dynamic and temperature distribution of membrane. The results provide certain instruction to PEMFC design and manufacture. Models established in this paper are to some extent transplantable and universal. Further steps can be taken to make optimization and design for power supply and vehicle systems.