Non intrusive diagnosis of polymer electrolyte fuel cells by wavelet packet transform

Fuel cell is a promising technology for both automotive and stationary applications. However, its reliability and its lifetime remain major hurdles to its wide access to these markets.It is therefore necessary to develop reliable diagnosis tools adapted to these two applications’ requirements. More particularly, online and real time tools for diagnosis will permit an early faults diagnosis and therefore an increase of the system reliability and performance.Most of the existing fault diagnosis methodologies in fuel cells require the knowledge of numerous parameters that may lead to a special inner parameter monitoring setup, which is difficult, even impossible to obtain, considering constraints like fuel cell stacks’ geometry. Moreover, considering the final fuel cell stack end-uses, for instance in transportation applications in which the “on-board” instrumentation has to be minimized, a model using a minimal number of parameter is highly desirable.In this paper, a simple and low-cost flooding diagnosis method applied to a PEFC (Polymer Electrolyte Fuel Cell) is described. This method only uses the stack voltage and can be adapted to a large set of fuel cell configurations and applications.Coming from the signal-processing domain, the diagnosis consists in a signal feature extraction by multiscale decomposition using discrete wavelet transform, followed by fault identification and classification. Results obtained in this work showed that the wavelet analysis method allows the identification of the flooding based on the patterns obtained from the wavelet packet coefficients.The application of wavelet theory to fuel cell diagnosis is innovative and very promising and the experimental results obtained in this study proved its feasibility and reliability to classify correctly PEFC experimental states into flooded and non-flooded state of health.     

Diagnostic tools for PEMFCs: from conception to implementation

By detecting and identifying degradation mechanisms, diagnostic tools are essential in avoiding premature ageing of PEM Fuel Cells. Indeed, the diagnosis of hazardous situations ensures the optimal management of operating conditions. This paper proposes several guidelines for choosing, designing and applying diagnostic tools for PEMFCs, focussing on developing objective criteria allowing an actual validation of the results. At the conceptual stage, methods to ensure the database representativeness of different degrees of flooding and drying, two typical faults in the PEM fuel cell, are discussed, and simple equations are given to estimate the relative humidity in the stack under applied operating condition. After the diagnostic tool has been realised, indicators to evaluate fault diagnosis performances are proposed. Implementation ability may be evaluated by cost criteria, which include equipment, consumed energy and consumed time. This paper demonstrates that a practical comparison of diagnosis methods is possible and provides new perspectives for establishing a benchmark in the diagnosis of fuel cells.     

Current density distribution in PEFC

The determination of the current distribution in a polymer electrolyte fuel cell (PEFC) is of great practical importance to optimize the process parameter such as the flow field design, the humidification of reaction gases and the utilization of the fuel gas. In this paper, subcells approach is used to measure current density distribution in PEFC with an active electrode area of 30 cm². Fuel cell performances determined under different operation conditions clearly indicate that the water balance influences the cell performance most significantly. Furthermore, it is interesting to note that under certain condition both membrane drying and electrode flooding are shown simultaneously inducing performance decaying.     

A fault diagnosis model for proton exchange membrane fuel cell based on impedance identification with differential evolution algorithm

An effective online fault diagnosis system is of great significance to improve the reliability of fuel cell vehicles. In this paper, a fault diagnosis model for proton exchange membrane fuel cells is proposed. Firstly, the tests of electrochemical impedance spectroscopy under different fault types (flooding, drying, air starvation) and fault degrees (minor, moderate, severe) are carried out, and each polarization loss of the fuel cell is denoted by an equivalent circuit model (ECM). Then, the parameters of the ECM are identified by the proposed random mutation differential evolution algorithm. Furthermore, the parameters identified under different fault conditions are used to train and test a probabilistic neural network-based fault diagnosis model. The fault diagnosis model achieves diagnosis accuracies of 100% for the fault type and 96.67% for the fault degree. By setting operating conditions with different fault degrees, the fault diagnosis model proposed in this paper can realize the fault type and fault degree diagnosis, effectively avoiding the misjudgment of fault types, and is effective for improving the reliability of the fuel cell system.     

Impedance-based diagnosis of polymer electrolyte membrane fuel cell failures associated with a low frequency ripple current

This work deals with a diagnosis of cathode flooding and membrane drying associated with a low frequency ripple current of a polymer electrolyte membrane fuel cell (PEMFC) based on impedance measurement on 12 single cells using electrochemical impedance spectroscopy (EIS). Average values of the identified model parameters obtained from direct measurement of the impedance curves of 12 single cells obtained after cycling for hours at variable frequencies, it has been found that impedance magnitude of a fuel cell injecting a low frequency ripple current (100 Hz) increased when compared with those injecting high frequency ripple currents (1 kHz and 10 kHz). Based on these investigations, additional impedance measurements are directly conducted to gain insight into cathode flooding and membrane drying concerning a low frequency ripple current. Regardless of operating frequency of ripple current, two PEMFC failures lead to an increase in the impedance magnitude in comparison with that of a fresh cell. Specifically, it is shown that a low frequency ripple current more accelerates the PEMFC degradation associated with two PEMFC failures.     

New magnetic field analyzer device dedicated for polymer electrolyte fuel cells noninvasive diagnostic

Inside the Fuel Cell, the magnetic field distribution can indicate normal or abnormal operation and therefore provides an effective diagnosis approach. The magnetotomography is the only noninvasive current density mapping method and is based on the measurement of the external magnetic field of the fuel cell stack. The present work addresses the development of a new magnetic field analyzer device devoted to assess the current density distribution inside the Fuel Cell, within the surrounding external magnetic field. The proposed magnetic field analyzer associates magnetic sensors with a ferromagnetic circuit, which is essentially different in comparison with other methodologies proposed until now. Providing a higher magnetic field variation at the level of magnetic sensors, this new approach enables a more accurate analysis of the current distribution inside the Fuel Cell. This study considers the Proton Exchange Membrane Fuel Cell case.     

Relationship between pressure drop and cell resistance as a diagnostic tool for PEM fuel cells

An increase in pressure drop, particularly on the cathode side of PEM fuel cell, is a reliable indicator of PEM fuel cell flooding, while an increase in cell resistance is a reliable indicator of fuel cell drying. By monitoring both pressure drop and cell resistance in an operational fuel cell stack it was possible to diagnose either flooding or drying conditions inside the stack. These parameters may be used for making decisions on corrective actions.     

Fractional order model for diagnosis of flooding and drying of the proton exchange membrane fuel cell

The diagnosis and control of PEMFCs hydration states depend on the reliable models and methods of monitoring of system operating. Impedance spectroscopy was generally used to describe fuel cell systems and derived impedance models. This study investigated the characterization and diagnosis of fuel cells by using fractional order impedance model as an explicit transfer function and factor design methodology (DOE) to determine the model parameters. The physical parameters appeared very sensitive to humidity and then used for monitoring and diagnosing of fuel cells. The proposed model is suitable to represent Randles impedance model equivalent electrical circuit enhanced by CPE, with the ability to generate the Nyquist impedance spectra easily for all conditions of relative humidity and operating time.The comparison between the literature experimental impedance spectra in both cases (drying and flooding), and the spectra simulated by the explicit fractional order impedance model demonstrated that the proposed model was robust and reliable and can, therefore, be integrated into the PEMFCs water management system.     

Online humidification diagnosis of a PEMFC using a static DC–DC converter

This paper deals with the online checking of the humidification of a Proton Exchange Membrane Fuel Cell (PEMFC). Indeed, drying or flooding can decrease the performance of the PEMFC and even lead to its destruction. An online humidification diagnosis can allow a real-time control. A good indicator of the membrane humidification state is its internal resistance. As known, the membrane ionic conductivity increases with the membrane water content. This resistance can be calculated at high frequency by dividing the voltage variation by the current variation. The proposed scheme makes use of measurements of current and voltage ripples coming from the association of a static DC–DC converter and the fuel cell. The experiment thus consists in computing the internal resistance in wet and dry conditions.     

Flooding and dehydration diagnosis in a polymer electrolyte membrane fuel cell stack using an experimental adaptive neuro-fuzzy inference system

Today the need for fault diagnosis in polymer electrolyte membrane fuel cells (PEMFCs) is felt more than ever to increase the useful life and durability of the cell. The present study proposes an indirect in-situ experimental-based algorithm for diagnosing the moisture content issues in a three-cell stack. Three adaptive neuro-fuzzy inference systems (ANFIS) approximate the system outputs (cells voltages, cathodic and anodic pressure drop) in normal conditions. The values of Pearson's correlation coefficients (0.998, 0.983, and 0.995 for outputs, respectively) show the high quality of the modeling. In unknown operating conditions, the residuals of experimental and ANFIS values are compared with obtained deviation thresholds (0.0735 V, 0.0092 bar, and 0.0047 bar for the outputs, respectively) to determine the cathode/anode flooding, membrane dehydration, or normal status. This method is helpful in commercial applications for diagnosing more than 50% of PEMFC faults because it uses accessible parameters and has low-processing demands.     

Proton exchange membrane fuel cell performance prediction using artificial neural network

Polarization curves remain one of the parameters used to check the performance of fuels in terms of efficiency and durability. This investigation explores the application of artificial neutral network (ANN) to determine the voltage and current from a proton exchange membrane fuel cell having membrane area of 11.46 cm². Performance predictability for the group method of data handling (GMDH) as well as feed forward back propagation (FFBP) neutral networks were employed for the estimation of the current and voltage obtained from the Proton Exchange Membrane Fuel cell under investigation. The investigation presented models with good predictions even though GMDH neural network performed better than the FFBP neural network. The study therefore proposes the GMDH neural network as the best model for predicting the performance of a Proton Exchange Membrane Fuel cell. It was further deduced that an increase in reactant flow rate has direct effect on the performance of the fuel cell but this is directly proportional to the total irreversibilities in the cell hence to operate fuel cell economically, it is imperative that the hydrogen flow is made lower compare to the oxygen flow rate. This in effect will reduce the pumping power required for the flow of the fuel hence reducing the net loss in the cell.     

Investigation of the effect of cathode stoichiometry of proton exchange membrane fuel cell using localized electrochemical impedance spectroscopy based on print circuit board

Proton Exchange Membrane Fuel Cell can have a large active area, and the working condition in different areas can be entirely different. Localized electrochemical impedance spectroscopy can directly observe the proton exchange membrane fuel cell internal reaction conditions. In this work, localized electrochemical impedance spectroscopy test system based on print circuit board is implemented in a 50 cm² multi-channel serpentine flow fields. The localized electrochemical impedance spectroscopy performances of different segments with different cathode stoichiometry (1.8, 2.3 and 2.8) at different current density (100  mA cm⁻², 500  mA cm⁻² and 900 mA cm⁻²) are studied. The result demonstrates that the fuel cell may suffer from local drying and flooding at the same time. To make full use of the potential of a fuel cell, a suitable cathode stoichiometry should be identified to control the drying of the inlet and the flooding of the outlet at the same time. It is shown that a cathode stoichiometry of 2.3 is close to the optimum cathode stoichiometry to keep the fuel cell in good consistency without gas waste. Besides, a current density distribution measurement is performed to verify the conclusions of this work.     

Characteristic simulation and numerical investigation of membrane electrode assembly in proton exchange membrane fuel cell

This study analyzes the characteristic numerical analysis of membrane electrode assembly in Proton Exchange Membrane Fuel Cell (PEMFC) with bipolar plate, flow channel, gas diffusion electrode, and proton exchange membrane. The numerical solution focuses on discussing the effects of different parameters, including permeability, porosity, and operation voltage, on various mass fractions, current-voltage curve, and power-voltage curve.The results show that as the porous medium with high gas permeability is an important factor that affects the mass fraction of hydrogen. Regarding the analyses of various porosities, the fuel cell performance can be effectively promoted with larger ratio of porosity and permeability. However, increasing the porosity will affect the electrical conductivity and increase the flooding of water, which will block the flow channel and reduce efficiency.     

Study of hybrid energy system coupling fuel cell,solar thermal system and photovoltaic cell

The present work examines the combination of solar energy systems with Fuel cell. Indeed, fuel cells are green storage systems without any pollution effects. They are supplied by oxygen and hydrogen to produce electricity. That is why it is inescapable to find a source of hydrogen in order to use fuel cell. Several techniques can be adopted to produce hydrogen depending on the availability and the cost of the sources. One of the most utilized techniques is electrolysers. They allow to obtain hydrogen from water by several technologies among them proton exchange membrane (PEM) which is considered in this work. On the other hand, electrolysers need electrical power to operate. A green-green energy system can be constructed by using a renewable energy source to supply fuel cell trough electrolysers. A comparison between two solar systems (Photovoltaic and Parabolic Trough) coupled to fuel cell is performed. A case study on the Lebanese city of Tripoli is carried out. The study shows the performance of each of both combined systems for different parameters and proposes recommendations depending on the considered configuration.     

Measurement of the water transport rate in a proton exchange membrane fuel cell and the influence of the gas diffusion layer

Water management in a PEM fuel cell significantly affects the fuel cell performance and durability. The gas diffusion layer (GDL) of a PEM fuel cell plays a critical role in the water management process. In this short communication, we report a simple method to measure the water transport rate across the GDL. Water rejection rates across a GDL at different cathode air-flow rates were measured. Based on the measurement results, the fuel cell operating conditions, such as current density, temperature, air stoichiometry and relative humidity, corresponding to membrane drying and flooding conditions were identified for the particular GDL used. This method can help researchers develop GDLs for a particular fuel cell design with specific operating conditions and optimize the operation conditions for the given PEM fuel cell components.     

Impacts of reactant flow nonuniformity on fuel cell performance and scaling-up: Comprehensive review,critical analysis and potential recommendations

Fuel Cells (FCs) have witnessed phenomenal improvements in operation and utilization for different stationary and mobile applications. Scaling up limitations of FCs and their integration restrictions into high energy applications because of maldistribution of the reactants’ (fuel and oxidant) flow become among the major drawbacks. The relevant non-uniform electrochemical reactions may result in the FC performance degradation and decrease in lifetime. Therefore, this paper aims at introducing a comprehensive review on the advances in the methods of flow distribution in FCs. The levels in FC design either individual cell or FC stack that introduce non-uniformities are highlighted. The negative impacts on the FC performance, mainly the thermal and water management aspects, have been explicitly introduced. The consequent phenomena the FC experiences such as non-uniform heating, water flooding and membrane drying are presented. Based on the literature review, the critical insights and recommendations are provided alongside a suggestion of a cellular level flow distributor design to be investigated in future studies.     

A review of the main parameters influencing long-term performance and durability of PEM fuel cells

This paper presents an overview of issues affecting the life and the long-term performance of proton exchange membrane fuel cells based on a survey of existing literature. We hope that this brief overview provides the engineers and researchers in the field with a perspective of the important issues that should be addressed to extend the life of next-generation fuel cells. Causes and fundamental mechanisms of cell degradation and their influence on long-term performance of fuel cells are discussed. Current research shows that main causes of short life and performance degradation are poor water management, fuel and oxidant starvation, corrosion and chemical reactions of cell components. Poor water management can cause dehydration or flooding, operation under dehydrated condition could damage the membrane whereas flooding facilitates corrosion of the electrodes, the catalyst layers, the gas diffusion media and the membrane. Corrosion products and impurities from outside can poison the cell. Thermal management is particularly important when the fuel cell is operated at sub-zero and elevated temperatures and is key at cold start-ups as well as when subjected to freezing conditions.     

MATLAB-based simulator of a 5 kW fuel cell for power electronics design

In the last few years, renewable energies have been encouraged by worldwide governments to meet energy saving policies. Among renewable energy sources, fuel cells have attracted much interest for a wide variety of research areas. Since combined heat-power generation is allowed, household appliances are still the most promising applications. Fuel cell-based residential-scaled power supply systems take advantage by simultaneous generation of power and heat, reducing the overall fossil fuel consumption and utilities cost. Modelling is one of the most important topic concerning fuel cell use. In this paper, a measurement-based steady-state and dynamic fuel cell model is presented. The parameters identification procedure is analyzed and the MATLAB/Simulink implementation is shown. The proposed modelling approach is implemented on a 5 kW Proton Exchange Membrane Fuel Cell. As shown by the comparison between experimental and simulation results, the model error is restricted to ±1%, corresponding to a maximum absolute model error of 0.6 V.     

Performance assessment of a four-pass serpentine proton exchange membrane fuel cell with non-humidified cathode and cell state estimation without special measurement

Proton exchange membrane fuel cells are promising electrochemical energy conversion devices especially important for mobile technologies, including the automotive industry thanks to their quick start-up, low operation temperature, and relatively higher energy density characteristics. However, cell performance depends on many parameters like reactant temperature and humidification ratio, cell operating temperature, reactant feeding pressure, and flow field. In this study, the performance of a 50 cm² active area four-pass serpentine flow field hydrogen-air proton exchange membrane (PEM) fuel cell experimentally investigated for various cell operating temperatures and reactant back pressures without humidification on the cathode side. Dehydration or flooding condition of the cell is showed to be determined with tafel slope, limiting current density and types of voltage losses without using a special measurement. The results show that flooding, which is called mild flooding, is possible to be seen even at high cell temperature in a non-humidified cathode fuel cell, in case of exceeding operating pressures. Behavior of cell parameters under mild flooding and ongoing severe flooding are different from each other. Pressure increase at above 45 °C operating temperature is seen to served higher power output. However, at low back pressure with escalated operating temperature doesn't result with a substantial increase on performance since less amount of water is produced as a product of reaction causing membrane dehydration at relatively low current density levels thus increasing ohmic loss.