质子交换膜燃料电池热管理系统建模及故障仿真

文章以质子交换膜燃料电池（Proton Exchange Membrane Fuel Cell,PEMFC）系统为研究对象,分析系统中各组成部件的工作机理,在MATLAB/Simulink软件中搭建了燃料电池电堆电压、阴极、质子交换膜、阳极以及温度的数学机理模型,同时使用Simulink/Simscape物理建模平台搭建热管理系统的物理模型,将两种模型集成为完整的PEMFC系统仿真模型。在所搭建的热管理系统模型中注入典型故障：散热器风扇故障和冷却液流量不足故障,对各故障模式下的燃料电池性能进行了分析。仿真结果表明：PEMFC系统模型结果与试验结果基本一致,验证了模型的合理性;通过对热管理系统故障进行仿真,可以清楚地了解故障发生的机理,为其故障诊断提供了参考依据。     

考虑环境温湿度的空冷PEMFC最佳工作温度研究与控制

空冷型质子交换膜燃料电池(PEMFC)属于阴极开放式燃料电池,无外部增湿装置,因此空冷型PEMFC阴极入口处空气的温度和湿度必然对燃料电池工作性能有着不可忽视的影响。通过实验研究空冷型PEMFC最佳工作温度与环境温湿度及输出电流之间的关系,分析不同环境温湿度和输出电流对空冷型PEMFC最佳工作温度的影响。最后设计空冷型PEMFC控制系统,根据得到的不同环境温湿度下的空冷型PEMFC最佳工作温度曲线,采用PID控制方法实现不同温湿度环境条件下的最佳工作温度控制。     

燃料电池运行控制参数影响规律仿真分析

基于Simulink平台,利用Thermolib工具包搭建Ballard公司的Mark V PEMFC分析模型,模型包括质子交换膜燃料电池(proton exchange membrane fuel cell,PEMFC)电堆模块、阴极供气系统模块、阳极供氢系统模块、冷却循环系统模块及控制系统模块等部分,通过试验数据对模型进行验证。利用搭建的模型研究电堆运行控制参数,如电堆温度、膜湿度、进气压力及压差等对PEMFC输出电压及功率的影响。研究结果揭示各运行控制参数对PEMFC电堆性能的影响,对PEMFC控制策略的开发有一定的指导意义。     

基于PEMFC分布式发电系统的动态特性分析

分析了质子交换膜燃料电池(PEMFC)的机理模型,在此基础上运用MATLAB的Simulink仿真工具,建立了PEMFC发电系统带负载模型。通过仿真,分析了负载对PEMFC电堆的各项动态特性(燃料的流量、效率、输出电压等)的影响,以及DC/DC、负载端的电压响应。仿真结果中负载电压呈三相交流正弦波形,表明搭建的整个PEMFC发电系统是基本正确的,为实现PEMFC并网的实时分析和动态优化提供了理论依据和参考方法。     

气体扩散层厚度对PEMFC性能的影响

质子交换膜燃料电池(PEMFC)的气体扩散层(GDL)厚度对燃料电池的输出性能有重要影响。文章利用多物理场直接耦合分析软件(COMSOL Multiphysics 5.0),在电池温度为70℃的条件下,对4种不同厚度的GDL进行模拟分析,并在相同的操作条件下,得到了4组极化曲线、阴极氧气浓度、阴极水浓度、阳极氢气浓度以及电流密度的变化趋势图。对比分析4组变化趋势图后发现:GDL的厚度越小,燃料电池的性能越好;GDL的厚度对阳极氢气的浓度分布影响不大;当GDL的厚度增大时,产生的液态水会堵塞GDL的孔隙,降低GDL的孔隙率。     

变工况对带涡流发生器的PEMFC性能的影响

质子交换膜燃料电池(PEMFC)是一种高效的能量利用装置。为了提高其工作性能,在其中加装涡流发生器,并研究工况对其性能的影响,对其进行了单因素和多因素影响分析,利用响应面法建立数学关系式。结果表明：加装涡流发生器,可以明显改善PEMFC温度均匀性、提高燃料利用率、改善通道排水,对燃料电池的性能有明显提升,电压为0.4 V时电流密度提升了55.4%;在所选区间内温度为65℃,相对压力为100 kPa,湿度为60%,化学计量比为2.50时,燃料电池的功率密度最大。     

PEMFC电堆建模及特殊工况下的动态分析

以包括冷却液通道、阴/阳极气体通道、MEA等4个控制体的PEMFC单池模型为基础,引入了与单池位置相关的反应气压力、水含量和温度的数学描述方法,建立了一种可以体现单池性能差异性的半机理半经验电堆动态模型.在此模型基础上,详细分析了电堆内重要物理量(温度、水含量和输出电压等)在特殊运行工况下(如启动、制动和怠速等)的动态特性.     

基于最大净功率输出的PEMFC阴极供气系统优化控制研究

通过建立质子交换膜燃料电池（PEMFC）阴极供气系统数学模型,分析空气压缩机电压和背压阀开度对系统净功率输出的影响;针对负载电流变化,研究PEMFC系统对应的最优过氧比和最优阴极压力,建立最大输出净功率-过氧比-阴极压力寻优表;考虑过氧比和阴极压力之间的耦合关系,基于辨识出的传递函数矩阵,设计针对空气压缩机电压和背压阀开度的前馈解耦控制器,优化氧气供给和压力控制,并进行相应的仿真验证。结果表明,所提解耦控制器能有效减小过氧比和阴极压力之间的耦合影响,在实现最大净功率闭环控制的同时,具有更快的响应速度和更小的超调量。     

空冷自增湿燃料电池最优控制方法研究

通过对影响质子交换膜燃料电池(PEMFC)输出性能因素的分析,得出PEMFC电堆工作温度、电堆输出电流是影响PEMFC输出性能的主要因素。在输出电流一定的情况下,电堆工作温度是影响PEMFC输出电压的主要因素。为实现对空冷自增湿PEMFC的最优控制,采用实验测试及数据拟合方法,得到PEMFC电堆最优温度与输出电流的函数关系式,通过控制PEMFC电堆工作在最优温度,以实现PEMFC输出电压的最优控制。实验测试表明,该控制方法简单实用、控制效果优越,可为空冷自增湿PEMFC的最优控制提供具有实用价值的控制方法。     

阴极挡板排列对PEMFC反应物输运和性能的影响

为了改善质子交换膜燃料电池(PEMFC)的性能,采用流道内使用挡板堵塞的方法,以增强反应气体向催化层的传质。建立了一个三维、两相、稳态的PEMFC数值模型,研究了凸字排布、顺排和逆排这3种不同阴极流道挡板的排布方式对PEMFC性能的影响,并与无挡板常规流场进行对比,然后在最佳排布方式的基础上研究了挡板形状(矩形、梯形和半圆形)对PEMFC性能的影响。结果表明：PEMFC阴极流道挡板顺排性能最好,相较于无挡板常规流道,净功率提升了14.3%;使用梯形挡板的PEMFC性能最好,相较于无挡板常规流道,净功率提高了16.4%。     

Investigation of the recoverable degradation of PEM fuel cell operated under drive cycle and different humidities

Recoverable degradation of a proton exchange membrane fuel cell (PEMFC) under different relative humidities (RHs) after a whole night rest was investigated. A single cell was operated under drive cycle to simulate the working conditions of fuel cell vehicle. It was found that the cell performance decreased after 5 h operation and recovered mostly after one night rest at higher humidities, i.e. 100%, 75% and 50% RH for both cathode and anode sides; while continuous decrease took place at lower humidity, 35%RH. Polarization curve, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted before and after every 5 h drive cycle for investigating the mechanism of the recoverable degradation. It was found that water content, current density and thermal management might be the main contributions to the performance degradation, by impacting the membrane conductivity, internal resistance, electrode kinetics, and catalyst utilization. A good understanding of voltage recovery phenomenon after several hours rest and its effect on durability will be helpful in improving the reliability and durability of PEMFC.     

Electrochemical impedance analysis with transmission line model for accelerated carbon corrosion in polymer electrolyte membrane fuel cells

The effects of varying the applied voltage and relative humidity of feed gases in degradation tests of polymer electrolyte membrane fuel cells (PEMFCs) were analyzed using electrochemical impedance spectroscopy (EIS). A transmission line model that considers the proton-transport resistance in the cathode catalyst layer was used to analyze impedance spectra obtained from degraded PEMFCs. As the applied cell voltage was increased from 1.3 to 1.5 V to induce accelerated degradation, the cell performance decayed significantly due to increased charge- and proton-transfer resistance. The PEMFC degradation was more pronounce at higher relative humidity (RH), i.e. 100% RH, as compared with that observed under 50% RH. Furthermore, changes in the charge transfer resistance of the electrode accompanied changes in the ionic conductivity in the PEMFC catalyst layer. Although the initial ionic and charge-transfer resistances in the catalyst layer were lower under higher RH conditions, the impedance results indicated that the performance degradation was more significant at higher water contents in the electrode due to the consequential carbon corrosion, especially when higher voltages, i.e. 1.5 V, were applied to the PEMFC single cell.     

Rapid degradation characteristics of an air-cooled PEMFC stack

Durability is one of the obstacles to the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) stacks. Understanding its decay behavior is a prerequisite for improving durability. In this study, rapid degradation characteristics of an air-cooled PEMFC stack are investigated. Due to the simultaneous presence of various degradation sources, the maximum power of the PEMFC stack has been reduced by 39.6% after just 74.6 h of operations. Performance degradation characteristics are sought by analyzing the cell voltage, temperature distribution, ion chromatography, and surface morphology of the gas diffusion layer. The result shows that abnormal cell voltage and temperature distribution can reflect the problematic location. The fluoride ion emission rate is 0.111 mg/day, which proves that the membrane has been seriously degraded. Contact angle reduction and impurities attached to the surface of the gas diffusion layer lead to the water management failure. It is also found that the main factor for performance degradation could be different under different current conditions. And more information can be found under higher current conditions during monitoring the decay of PEMFCs. This study helps to deepen the understanding of performance degradation characteristics.     

Understanding and approaches for the durability issues of Pt-based catalysts for PEM fuel cell

The state-of-art understanding of durability issues (the degradation reasons and mechanisms, the influence of working conditions, etc.) of Pt-based catalysts for proton exchange membrane fuel cell (PEMFC) and the approaches for improving and studying catalyst durability are reviewed. Both carbon support and catalytic metals degrade under PEMFC conditions, respectively, through the oxidation of carbon and the agglomerate and the detachment from support materials of catalytic metals, especially under unnormal working conditions; furthermore, the degradation of carbon support and catalytic metals interact with and exacerbate one another. The working temperature, humidity, cell voltage (the electrode potential and the mode applied on the electrode), etc. can influence the catalyst durability. Carbons with high graphitization degree as support materials and alloying Pt with some other metals are proved to be effective ways to improve the catalyst durability. Time-effective and reliable methods for studying catalyst durability are indispensable for developing PEMFC catalysts.     

Fault tree analysis for PEM fuel cell degradation process modelling

For transportation applications, Proton Exchange Membrane fuel cells (PEMFC) are considered to be the most promising fuel cell technology due to their low operating temperature and pressure resulting in a possible quick start-up. However, to implement them in transportation systems, their reliability should be improved. In the present work, a single fuel cell is considered. It is composed of a membrane, catalyst layers (anode and cathode electrodes) and diffusion layers (anode and cathode electrodes). Those layers are considered as the critical components of the cell. Modelling the process degradations of those components is a great issue. In this work, Fault Tree (FT) is used for this modelling for two main reasons. At first, FT helps to model clearly and intuitively the different causal relations of the degradation mechanisms. Secondly, FT allows quantifying components specific degradations, and their effects on the global degradation of the cell. The cell is considered non repairable. Degradation modelling needs knowledge about mechanisms involving components failures. For 1000 simulations of 100 h operation in cycling conditions, the results of the FT show the most important degradations effects on the global degradation of the cell. This work also proposes degradation probability estimates for some specific events.     

Simulation study on magnetic field distribution of PEMFC

As a promising next-generation energy source, proton exchange membrane fuel cell (PEMFC) still suffers from durability and reliability issues, where PEMFC performance will decay during its operation. In this study, a three-dimensional, multi-component and multi-physics PEMFC model is developed to investigate the effect of PEMFC performance degradation on its external magnetic field. By comparing simulation results and experimental data, the capability of the developed model in simulating magnetic field due to PEMFC current is demonstrated. With developed model, different PEMFC degradation mechanisms, including flooding, dehydration, PEMFC aging are simulated, and the amplitudes and distributions of magnetic field under different mechanisms are investigated. Moreover, considering local defects may happen in practical PEMFC systems, its influence on magnetic field distribution is also studied. From the results, the correlation between PEMFC performance degradation and its magnetic field distribution is clarified, which will be beneficial for researches utilizing PEMFC magnetic field for analyzing PEMFC performance variation.     

Study on voltage clamping and self-humidification effects of pem fuel cell system with dual recirculation based on orthogonal test method

Durability and reliability are still major challenges of vehicular polymer electrolyte membrane fuel cell (PEMFC) systems. With exhaust gas recirculation on both the anode and cathode sides, two important functions can be achieved: the voltage clamping in low current density, and the self-humidification without any external humidifiers. The former restrains catalyst decay in small load working conditions, and the latter is beneficial for improving the cold-start ability. In this study, dynamic performances and stable characteristics of a fuel cell system with dual exhaust gas recirculation are firstly experimentally studied using an orthogonal test method. System parameters, including humidification temperature of cathode external humidifier, fresh air stoichiometric ratio (SR), current density, cathode and anode recirculation pump speeds, are regarded as key factors in the experiments based on the testing conditions of the test-bench. Two four-factor and three-level orthogonal tables are designed, and the effects of key factors on system performance indices (average cell voltage, relative humidity (RH) at cathode inlet, high frequency resistance (HFR), oxygen concentrations at cathode inlet and outlet, and the concentration difference between these two positions) are investigated. Results show that: (1) with the cathode recirculation, the cell voltage can be reduced in low current densities by coordinately adjusting the recycled gas flow and reducing fresh air SR; (2) with the dual recirculation, the fuel cell membrane can be well hydrated, and system performance only shows 3% reduction compared with a system with an external humidifier; (3) the difference between the oxygen molar concentration at the inlet and outlet of cathode gas channels becomes small using dual recirculation.     

Model predictive control of water management in PEMFC

Water management is critical for Proton Exchange Membrane Fuel Cells (PEMFC). An appropriate humidity condition not only can improve the performances and efficiency of the fuel cell, but can also prevent irreversible degradation of internal composition such as the catalyst or the membrane. In this paper we built the model of water management systems which consist of stack voltage model, water balance equation in anode and cathode, and water transport process in membrane. Based on this model, model predictive control mechanism was proposed by utilizing Recurrent Neural Network (RNN) optimization. The models and model predictive controller have been implemented in the MATLAB and SIMULINK environment. Simulation results showed that this approach can avoid fluctuation of water concentration in cathode and can extend the lifetime of PEM fuel cell stack.     

Research on two‐phase flow considering hydrogen crossover in the membrane for a polymer electrolyte membrane fuel cell

Hydrogen crossover has an important effect on the performance and durability of the polymer electrolyte membrane fuel cell (PEMFC). Severe hydrogen crossover can accelerate the degradation of membrane and thus increase the possibility of explosion. In this study, a two‐phase, two‐dimensional, and multiphysics field coupling model considering hydrogen crossover in the membrane for PEMFC is developed. The model describes the distributions of reactant gases, current density, water content in membrane, and liquid water saturation in cathode electrodes of PEMFC with intrinsic hydrogen permeability, which is usually neglected in most PEMFC models. The conversion processes of water between gas phase, liquid phase, and dissolved water in PEMFC are simulated. The effects of changes in hydrogen permeability on PEMFC output performance and distributions of reactant gases and water saturation are analyzed. Results showed that hydrogen permeability has a marked effect on PEMFC operating under low current density conditions, especially on the open circuit voltage (OCV) with the increase of hydrogen permeability. On the contrary, the effect of hydrogen permeability on PEMFC at high current density is negligible within the variation range of hydrogen permeability in this study. The nonlinear relations of OCV with hydrogen diffusion rate are regressed.     

Novel in situ measurements of relative humidity in a polymer electrolyte membrane fuel cell

Miniature temperature/humidity sensors are incorporated into the graphite flowplates of a single cell polymer electrolyte membrane fuel cell (PEMFC) in order to measure the humidity profile along the serpentine channels of both anode and cathode in real time. The sensors show robust performance and importantly are able to recover after saturation. The key observation is a significant increase in relative humidity along the anode gas channel due to back diffusion of water from cathode to anode. Such measurements may be used to determine the water balance in the cell under a range of operating conditions to facilitate model validation and system optimisation.