| Proton exchange membrane fuel cell(PEMFC)is an electric powergeneration device which converts chemical energy of hydrogen into electric energy by electrochemical reaction.It has the advantages of high energy conversion,zero emission and no noise,etc.It is the core component to realize industrial application and commercial development of hydrogen energy.As a complex power generation system coupled with multi-substance and multi-phase changes,the modeling and simulation research of PEMFC has made great progress.However,there is still a lack of research for further investigation on the voltage undershoot phenomenon and the mechanism of dynamic substance change under transient loading conditions.The voltage undershoot has a significant influence on the performance and working life of PEMFC.Therefore,the dynamic performance of PEMFC is studied in this paper.Firstly,the global performance(steady and transient states)simulation model of PEMFC was established with the logic chain of the upstream and downstream control,namely,operating parameters,dynamic parameters and performance parameters.By studying the influence of operating parameters including stoichiometric ratio,gas back pressure,relative humidity and heat source temperature,on the dynamic parameters of gas concentration,water saturation,membrane water content and operating temperature,a control sub-model of operating parameters was established.Based on in-depth analysis of the internal mechanism of dynamic parameter transmission,the dynamic parameter transmission sub-model was established,also with considering other influence factors like electrochemical reaction,material phase change,power andthermal conversion,migration of electroosmosis effect.The dynamic undershoot process was divided into two stages: performance undershoot and performance recovery,which were modeled and characterized respectively.Based on the analysis of the above sub-models,a functional relationship model between operating parameters,dynamic parameters and output performance of PEMFC was established.Then,the simulation ability of the model was trained and verified by means of experiments and simulation methods.Based on the PEMFC single cell test platform and the MATLAB software in supercomputer platform,the single cell performance test experiment and the digital simulating operation system were respectively built up.Using the experimental data as training database,the steady-state performance and dynamic-state performance of the model were trained through calculating the minimum relative errors by genetic algorithm,and the relative errors are less than 2% and 0.3%respectively.A load current operating condition simulating New European Driving Cycle(NEDC)condition was taken into the model for a long period of full operating cycle simulation test,which aimed to verify the stability and applicability of the gas transfer calculation method of the model.Finally,based on the model,the transient performance and internal transimission mechanism of PEMFC were analyzed,and the methods of operation security and stability maintenance were studied and developed.The influence of operating parameters on dynamic voltage variation under transient load were studied.The variation of gas concentration in PEMFC,gas concentration transfer between layers and liquid water saturation distribution under transient load was analyzed,and the underlying mechanism of voltage undershoot was investigated.Based on the above rules,a method for safety and stability maintenance was proposed to prevent excessive voltage after loading,which was from two aspects of transient loading amplitude control and operating parameter control.The research content provides a new idea for the stability research of PEMFC operation. |
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