Optimization And Evaluation Of Output Performance For Water-cooling PEMFC Based On Internal Resistance Characteristics

Energy shortage is a serious problem facing the human development,while the reserve of traditional fossil energy are limited,and releasing a large number of polluting gases when they burn,so they haven’t been able to meet the requirements of green ecological development concept at the present time.Due to the advantages of clean and no pollution,low temperature rapid start,high power density and long service life,the technology of fuel cell power generation has gained bright prospects for its application and development.In the actual work of fuel cell,the fuel cell stack is the core component of the whole system,its internal water and heat management state is the key factor affecting the output performance of the system.In this paper,the water and heat management of fuel cell stack are studied in-depth.Firstly,according to the equivalent circuit model,the mechanism model of internal resistance and temperature and humidity operating conditions are established respectively in each characteristic section,the coupling model is established between the operating conditions,what the total resistance is the smallest is seen as the principal of simulation and optimization,the optimum temperature and humidity are obtained according to the different current densities,and the law of change is studying,the empirical formula is fitting,the foundation lays for the follow-up control.Secondly,againsting the disadvantages of long test time and big lag in the electrochemical impedance spectroscopy,the output performance optimization method based on frequency secant angle is proposed,the response signal of the high frequency transition frequency and the highest frequency of the two frequency points are detected,calculating the angle between the line connecting two points and real axis—frequency secant Angleα,and the ohmic resistance R_m is getted,a_优and R_m优are compared in optimal working condition,and then adjusting the control variables so that thea、R_m tends toa_优、R_m优,to optimize the output performance of fuel cell.Then,a quantitative calculation method for the degradation with internal resistance evaluation index is presented,the traditional EIS method has been improved,by the method of frequency sweep in the short frequency range,search for low frequency transition frequency point,the resistance of fuel cell stacks in different degradation levels were detected quickly,the empirical formula is fitted,the similarity degree was calculated using the curve similarity degree function,acquire the similarity degree difference of overall output performance by the center of gravity method,the evaluation of output performance is completed.Finally,experimental platform is set up,the assemblies degradation evaluation method is verified experimentally,the validity of the proposed algorithm is verified.