| Based on severe environmental problems and energy crises,China has put forward ambitious goals of "carbon neutrality" and "carbon peaking".Proton exchange membrane fuel cell(PEMFC)is gradually growing into a new power source for new energy vehicles due to its high efficiency,zero emissions,and low noise.However,PEMFC has a lot of room for growth from the performance of the stack itself,to the dynamic characteristics of the system,to the energy matching of the entire vehicle.This research is based on the object-oriented non-causal modeling language Modelica to jointly develop fuel cell stack models with different complexity,auxiliary subcomponent models and vehicle dynamics model.On the basis of these models,a threelevel simulation technology system of "stack-system-vehicle" is built,mainly for transient simulation of various typical dynamic conditions at different levels.The research work of this paper is summarized as follows:(1)A quasi-two-dimensional stack model of the fuel cell was established,fully considering the coupled transmission mechanism of "water-heat-gas-electricity" inside the cell and the research on the icing characteristics inside the cell.The model was verified by multiple sets of experiments,which matched well with the experimental data.The physical modeling principle of Modelica requires that each component has a complete flow resistance calculation.In view of the variability and complexity of the stack flow resistance,this paper establishes an input flow resistance calculation method based on the experimental data for fitting.Based on this model,the differences in cell performance under different operating conditions were explored.The results show that increasing the intake pressure and the stoichiometric ratio to a certain extent can increase the concentration of the catalyst layer reactants and reduce the activation loss of the cell;in addition,a higher intake relative humidity is beneficial to increase the water content of the membrane electrode electrolyte and improve the conductivity of protons,thereby improving performance.(2)The fuel cell system model is established.On the basis of the stack model,the sub-component models of the four major subsystems are coupled to build a relatively complete simulation system.Simulation of the hysteresis effect that may be caused by components including inertial parts such as air compressors under step load conditions is presented in this paper.The results show that without control optimization,the hysteresis effect time of air compressors is 2s,with PID(Proportion Integration Differentiation)control Algorithms can reduce the hysteresis effect to 0.1s or less.At the same time,under continuous loading conditions,the faster the loading rate,the more difficult it is to maintain the internal water dynamic equilibrium state,which in turn leads to worse performance when loading is completed.In addition,the transient performance of the sub-components represented by the air compressor and the back pressure valve is analyzed when the system undergoes step-change load conditions,and the dynamic matching of each sub-component provides a guarantee for the stable output of the stack.(3)The vehicle dynamics model of the fuel cell vehicle is established,two energy management strategies are proposed: one is based on the fuel cell power following,and another is based on the power battery SOC(State of Charge)state energy management.The vehicle model was used to simulate the NEDC(New European Driving Cycle)working conditions.The results show that the model has a good simulation ability for variable speed conditions.The first strategy has higher requirements on the dynamic performance of the vehicle itself.The second strategy limits the capacity of the power battery which needs to be slightly larger.For strategy one,further simulations of WLTC(World Light Vehicle Test Cycle)and CLTC(China Light-duty Vehicle Test Cycle)operating conditions were carried out,and the stack dynamic matching performance was good. |
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