Investigations On The Cold-Start Characteristics And Control Strategy Of Proton Exchange Membrane Fuel Cells

Proton Exchange Membrane Fuel Cell(PEMFC)has been widely concerned and vigorously promoted by society for its advantages of high efficiency and low pollution.But PEMFC has a high requirement in the working environment and needs to operate in a suitable temperature range to obtain better performance output.In a low-temperature environment,the output performance of PMEFC will change.In a sub-zero environment,starting failure will be caused by icing and other factors,reducing the battery’s durability.Therefore,cold starting has become a critical problem restricting the commercial development of PEMFC.An ideal process for starting PEMFC at a low temperature requires running the stack to the target temperature and minimizing the permanent performance damage caused by starting.To improve the performance of low temperature start-up,this thesis studies the start-up characteristics and strategy of PEMFC in a low-temperature environment by combining experiment and modelling.This study provides a deeper and comprehensive understanding of solving the problem of cold start and puts forward a fast,stable,and efficient cold start strategy based on the results.The main research contents of this thesis are as follows:(1)We designed and completed the experiment of cold start characteristics on the self-designed experimental platform.The initial performance of the healthy stack is tested,which can be used to compare the performance changes of the stack before and after startup.The variation of the stack’s output performance with temperature and the maximum output power at each operating temperature point is obtained.The critical temperature of the self-starting stack is obtained.By comparing the polarization curve and internal current distribution when the cold start is successful and fails,the key factors affecting the cold start are analyzed,which provides the direction for formulating and optimizing the startup strategy.(2)The sub-models were established to describe the temperature and water state in the stack according to the operating mechanism.The voltage empirical sub-model was established according to the polarization curve law,and the relevant empirical parameters were identified by the nonlinear least square method.According to the input-output relationship,the sub-models were connected,and the overall cold start model was built in the MATLAB/Simulink simulation environment.The experimental data verified the accuracy of the model.The variation of output power with current and temperature is further analyzed through model simulation.(3)Based on the experimental and model law,a multi-stage start-up scheme combining self-auxiliary heat is proposed to shorten the start-up time and improve the energy utilization rate.The maximum power loading method is proposed for the selfstarting stage of the stack.The simulation results show that the method can improve heat generation efficiency and accelerate start-up.An extreme value search algorithm was designed to track the maximum power point in real-time during start-up,and its accuracy was verified.Experiments verify the feasibility and superiority of the proposed cold start control strategy.The results of the start-up experiment and performance comparison show that the system has good start-up performance and does not cause significant damage to the stack.