Polymer Electrolyte Membrane Fuel Cell System Research Articles

Investigation of polymer electrolyte membrane fuel cell internal behaviour during long term operation and its use in prognostics

This paper investigates the polymer electrolyte membrane (PEM) fuel cell internal behaviour variation at different operating condition, with characterization test data taken at predefined inspection times, and uses the determined internal behaviour evolution to predict the future PEM fuel cell performance. For this purpose, a PEM fuel cell behaviour model is used, which can be related to various fuel cell losses. By matching the model to the collected polarization curves from the PEM fuel cell system, the variation of fuel cell internal behaviour can be obtained through the determined model parameters. From the results, the source of PEM fuel cell degradation during its lifetime at different conditions can be better understood. Moreover, with determined fuel cell internal behaviour, the future fuel cell performance can be obtained by predicting the future model parameters. By comparing with prognostic results using adaptive neuro fuzzy inference system (ANFIS), the proposed prognostic analysis can provide better predictions for PEM fuel cell performance at dynamic condition, and with the understanding of variation in PEM fuel cell internal behaviour, mitigation strategies can be designed to extend the fuel cell performance.

Techno-economic analysis of polymer electrolyte membrane fuel cell system configurations

The major constraints restricting wide-spread commercialization of fuel cell systems are both technical and economical. Many researchers have designed polymer electrolyte membrane (PEM) fuel cell system configurations, which are different in terms of energy utilization and cost. Therefore, it is imperative to determine the best system configuration in order to produce efficient and economically viable PEM fuel cell systems. This paper reports an exergy and economic analyses conducted on five different PEM fuel cell system configurations with a view to assess their performance. Thermolib – a tool box for MATLAB/Simulink designed for modelling and simulation of energy systems was used to model and simulate the operation of each of the systems (5 kW stack power, 40 cells and 0.25m2 active membrane area) and data obtained was used for the exergy analysis. It was found that largest exergy loss occurred in the fuel cell stack (over 90%). The overall exergy and energy efficiencies of the studied systems were between 24.23% to 30.18% and 47.77% to 59.48%, respectively. A hybrid PEM fuel cell system configuration was proposed and analyzed. It was found to have an overall exergy and energy efficiencies of 31.95% and 62.97%, respectively. The return-on-investment evaluated for each of the five studied PEM fuel cell system configurations as well as the proposed system configuration were 1–27% while the payback periods were 3–13 yrs. The proposed system configuration was found to have the best performance in terms of energy utilization and had the lowest cost per kilowatt net power.

Experimental study on dual recirculation of polymer electrolyte membrane fuel cell

Durability and start-up ability in sub-zero environment are two technical bottlenecks of vehicular polymer electrolyte membrane (PEM) fuel cell systems. With exhaust gas recirculation on the anode and cathode side, the cell voltage at low current density can be reduced, and the membrane can be humidified without external humidifier. They may be helpful to prolong the working lifetime and to promote the start-up ability. This paper presents an experimental study on a PEM fuel cell system with anodic and cathodic recirculation. The system is built up based on a 10 kW fuel cell stack, which consists of 50 cells and has an active area of 261 cm2. A cathodic recirculation pump and a hydrogen recirculation pump are utilized on the cathode and anode side, respectively. Key parameters, e.g., stack current, stack voltage, cell voltage, air flow, relative humidity on the cathode side, oxygen concentration at the inlet and outlet of the cathode side, are measured. Results show that: 1) with a cathodic recirculation the system gets good self-humidification effect, which is similar to that with an external humidifier; 2) with a cathodic recirculation and a reduction of fresh air flux, the cell voltage can be obviously reduced; 3) with an anodic recirculation the cell voltage can also be reduced due to a reduction in the hydrogen partial pressure, the relative humidity on the cathode side is a little smaller than the case with only cathode recirculation. It indicates that, for our stack the cathodic recirculation is effective to clamp cell voltage at low current density, and a self-humidification system is possible with cathodic recirculation. Further study will focus on the dynamic model and control of the dual recirculation fuel cell system.

Robust control of internal states in a polymer electrolyte membrane fuel cell air-feed system by considering actuator properties

Air stoichiometry, pressure, and relative humidity in the air-feed system of a vehicular polymer electrolyte membrane fuel cell (PEMFC) influence efficiency, durability and reliability. It is critical to develop robust control algorithms for these internal states to improve system performance. There is limited extant research on designing robust control algorithms that consider the three internal states as well as the constraints of real actuators, such as an air compressor, a membrane humidifier, and a back-up pressure valve (BPV). This study examines robust control strategies for the three internal states based on adaptive second order sliding mode (ASOSM) and nonlinear proportional-integral (NPI) feedback control algorithms. In the study, control targets are established based on stable properties of the PEMFC system. The study involves proposing and comparing five control strategies that are a combination of NPI and ASOSM algorithms. The following results are obtained: (1) the stable control targets for the three internal states are followed adequately by using an NPI or an ASOSM algorithm and differences only exists in dynamic processes; (2) with respect to the control of air stoichiometry, an NPI algorithm performs better than an ASOSM algorithm as chattering in air stoichiometry can be avoided and the convergence time to the target value is acceptable; (3) with respect to the control of cathodic pressure, an ASOSM algorithm performs better than an NPI algorithm as the overshoots in cathodic pressures can be effectively reduced; (4) with respect to the control of relative humidity, both NPI and ASOSM algorithms lead to a practical bang–bang strategy. The strategy that performs the best among the five strategies is selected, and the robustness of the selected strategy with respect to parameter uncertainties is verified.

(Invited) Advancements and Prospects of DOE Fuel Cell Research and Development Activities

The Fuel Cells program in the U.S. Department of Energy‘s (DOE) Fuel Cell Technologies Office (FCTO) supports research and development (R&D) of fuel cells for transportation, stationary and early market applications. The program seeks a balanced, comprehensive approach to developing fuel cells for near-, mid-, and longer-term applications. The program’s R&D portfolio is primarily focused on polymer electrolyte membrane (PEM) fuel cells as they relate to automotive applications. However, the R&D portfolio also includes longer term technologies, such as alkaline fuel cells, and higher temperature fuel cells like molten carbonate fuel cells for stationary applications. Cost and durability continue to be the key challenges to fuel cell commercialization. The cost projection for an 80-kWnet automotive PEM fuel cell system based on next-generation laboratory technology and operating on direct hydrogen is $53/kWnet when manufactured at high volume (500,000 units/year), with the program targeting a cost of $40/kW by 2020. Long-term competitiveness with alternative powertrains is expected to require further cost reduction to $30/kW, which represents the program’s ultimate cost target. A reduction in platinum group metal (PGM) loading and an increase in membrane electrode assembly (MEA) area power density are required to reduce material costs to the 2020 target. DOE focuses on funding R&D approaches for the development of highly active and durable catalysts that can reduce PGM content to below 0.125 g/kW. Commercial fuel cells are expected to use PGM-based catalysts in the near term; however, reaching cost competitiveness with conventional automobiles in the long-term will require a transition from PGM-based catalysts to PGM-free catalysts. To address this issue, the program launched a consortium called ElectroCat (for Electrocatalysis consortium), under the umbrella of DOE’s Energy Materials Network. ElectroCat aims to accelerate PGM-free catalyst and electrode development; it accomplishes this by coordinating relevant expertise and tools at the national labs. Beyond catalyst R&D, the program has also been able to demonstrate major advances in the development of durable, high-performance membranes that will allow fuel cells to operate for longer periods of time under harsh conditions. Additionally, improving durability while maintaining performance is critical to further enabling fuel cell commercialization. DOE independent validation of on-road fuel cell electric vehicles has shown a more than four-fold increase in the maximum projected durability of fuel cell systems, increasing from 950 hours in 2006 to over 4,100 hours in 2016 when projected to 10% voltage degradation. Further improvement is required to meet DOE’s durability 2020 target of 5,000 hours and ultimate target of 8,000 hours. Emphasis is placed on R&D that advances fuel cell performance and durability by addressing transport, degradation, and state-of-the-art cell component integration issues, as well as the need for new diagnostics, characterization tools, and models. FCTO recently established Fuel Cell Performance and Durability (FC-PAD), an R&D consortium led by a team of national laboratories, to directly address these topics. This core lab team also works with competitively selected industry and academic partners to advance the science and engineering of fuel cells, with a particular focus on developing durable, high-performance electrodes and MEAs.

Optimum Energy Management of PEM Fuel Cell Systems Based on Model Predictive Control

This work presents an optimum energy management framework, which is developed for integrated Polymer Electrolyte Membrane (PEM) fuel cell systems. The objective is to address in a centralized manner the control issues that arise during the operation of the fuel cell (FC) system and to monitor and evaluate the system’s performance at real time. More specifically the operation objectives are to deliver the demanded power while operating at a safe region, avoiding starvation, and concurrently minimize the fuel consumption at stable temperature conditions. To achieve these objectives a novel Model Predictive Control (MPC) strategy is developed and demonstrated. A semiempirical experimentally validated model is used which is able to capture the dynamic behaviour of the PEMFC. Furthermore, the MPC strategy was integrated in an industrial-grade automation system to demonstrate its applicability in realistic environment. The proposed framework relies on a novel nonlinear MPC (NMPC) formulation that uses a dynamic optimization method that recasts the multivariable control problem into a nonlinear programming problem using a warm-start initialization method and a search space reduction technique which is based on a piecewise affine approximation of the variable’s feasible space.The behaviour of the MPC framework is experimentally verified through the online deployment to a small-scale fully automated PEMFC unit. During the experimental scenarios the PEMFC system demonstrated excellent response in terms of computational effort and accuracy with respect to the control objectives.

Separation and Characterization of Overpotentials in Electrochemical Hydrogen Pump with a Reference Electrode

An electrochemical hydrogen pump (EHP) is a device employed for compressing hydrogen gas. The compression efficiency of the EHP, which operates by an isothermal process in principle, is theoretically higher than that of a conventional mechanical compressor, which operates by an adiabatic process. The structure of an EHP cell is similar to that of polymer electrolyte membrane fuel cell (PEMFC). In the EHP, compressing process is realized by imposing a potential difference to catalyst coated membrane (CCM) and completed by 3 steps: hydrogen oxidation reaction (HOR) at anode, conduction of hydrogen protons through membrane and hydrogen evolution reaction (HER) at cathode. Similar with PEMFC, overpotentials involved in EHP are categorized into two components: ohmic overpotential, mainly attributed to the conduction of protons through the membrane, and non-ohmic overpotential, which involves activation and concentration overpotentials. Due to the fast speed of hydrogen electrode reaction, ohmic overpotential is the main overpotential in the EHP. In order to reduce membrane resistance, bubbler humidifier same as that used in PEMFC system is conventionally utilized for humidifying membrane. However, different with PEMFC there is no water generation reaction occurs in the cathode side of EHP, the water at cathode dragged by hydrogen protons may be not enough for humidifying membrane at low current and high temperature conditions. Moreover, the effects of compression ratio (pressure of hydrogen at cathode) on overpotentials are important but not well discussed yet. In order to solve the problems which mentioned above, we supposed a different humidification method and employed a reference electrode for separating overpotentials. An internal humidification method is employed which is realized by storing liquid water in the cathode end plate shown in Fig.1. The liquid water directly humidifies membrane, leading to higher conductivity of membrane than that using a conventional bubbler humidifier [1]. This method is expected to balance water transport through membrane and keep membrane hydrated at high temperature. Electrochemical impedance spectroscopy (EIS) is introduced to clarify the effects of compression ratio on ohmic overpotential and non-ohmic overpotential. The compression ratio effects on overpotentials evaluated by EIS show following characteristics: For the part of ohmic overpotential, experimental results don’t show any dependence on compression ratio which suggests that water transport in EHP is more like diffusion process rather than convection process. On the other hand, non-ohmic overpotential decreases with increasing of hydrogen pressure of cathode. Separation results with reference electrode clearly shows that decreasing of non-ohmic overpotential occurs at cathode and it is attributed to the increasing of exchange current density of HER by increasing hydrogen pressure. Fitting I-V curves with a Volmer-Heyrovsy-Tafel expression [2] shows that the kinetic of HER and HOR are limited by diffusion process to/from electrode at anode/cathode. This is also confirmed by electrochemical impedance spectra data obtained at low frequency region. The concentration overpotential at anode is attributed to hydrogen diffusion through gas diffusion layer (GDL). In the EHP, in order to decrease hydrogen leakage, compression pressure supplied by end plates is set to 5MPa, which is much higher than common value (1~2MPa) used in PEMFC cell. At such a high compression pressure, GDL is compressed extremely, leading to small value of efficient gas diffusivity of hydrogen. Limiting current of anode calculated by hydrogen gas diffusion through GDL is less than 2A/cm2which agrees with the fitting results generally. The concentration overpotential at cathode is larger than that at anode. Frist, we suspected that water layer built at cathode may work as a mass transfer barrier for hydrogen gas and lead to large mass transfer resistance. However, an additional experiment carried out with bubbler humidification showed even larger mass transfer resistance at cathode. It is clear that mass transfer of hydrogen at cathode is not limited by water layer. It is possible that hydrogen diffusion in catalyst layer leads to the high concentration overpotential. The structure of catalyst layer is assumed to consist of gas pores and aggregates of Pt/C covered by ionomer layers [3]. Hydrogen that produced at reaction sites of cathode need to diffuse through this ionomer layer. With the liquid water humidification, water content of ionomer layer increases [4] which enhances the permeability of hydrogen and decreases mass transfer resistance. Reference: [1] T. A. Zawodzinski Jr., T. E. Springer, and S. Gottesfeld. Journal of The Electrochemical Society, 1993, 140(7) 1981-1985. [2] P.M. Quaino, A.C. Chialvo, Electrochimica Acta, 2007(52) 7396–7403. [3] Firat C, Ajay K. Prasad, Journal of The Electrochemical Society, 2014,161 (6) F803-F813. [4] T. Sakai, E. Torikai. Journal of The Electrochemical Society, 1985, 132(6) 1328-1332. Figure 1

Zinc-Derived Microporous Structure in Non-Precious Metal Catalysts for Polymer Electrolyte Fuel Cell Cathodes

The kinetically sluggish oxygen reduction reaction (ORR) at the cathode of polymer electrolyte membrane fuel cells (PEFCs) requires higher content of platinum at the cathode than the facile hydrogen oxidation at the anode. Due to the scarcity and high cost of platinum, the development of inexpensive platinum group metal-free (PGM-free) ORR catalyst is one of the most urgent needs in the PEFC field. Transition metal-nitrogen-carbon (M-N-C) catalysts obtained by heat-treating transition metals, nitrogen, and carbon precursors have been viewed as the promising PGM-free catalysts for PEFC cathodes though not yet meeting all the performance characteristics required. High ORR activity, excellent mass-transport properties and practical long-term durability must be achieved simultaneously for PGM-free catalyst to replace platinum-based catalysts in the PEFC system. Specific catalyst precursors and heat-treatment conditions are critical to obtaining PGM-free catalysts with the desired structure. Iron- and cobalt-based zeolitic imidazolate frameworks (ZIFs), with uniformly distributed transition metals coordinated by N-containing ligands, have been viewed as highly suitable precursors for ORR catalysts. However, catalysts derived from these ZIFs often have low surface area and porosity, which are not conducive to efficient mass transport. On the contrary, ZIF-8, a zinc based ZIF, yields carbon with high surface area and porosity. Dodelet et al. used ZIF-8 as a microporous host for Fe and N precursors [1]. Following a heat-treatment at a relatively high temperature of 1050 ºC, they obtained an ORR catalyst with enhanced fuel cell performance. Unlike Fe and Co in Fe- and Co-based ZIFs, zinc in ZIF-8 is volatile during high-temperature treatment, likely acting as pore-forming agent. Base on that assumption, we used in this work a zinc salt instead of zinc ZIF as a precursor responsible for the formation of micropores in the catalyst. By using high heat-treatment temperature we also achieved more corrosion-resistant catalysts, while increasing the porosity and specific surface area from 315 m2 g-1 to 910 m2 g-1due to Zn evaporation. Fe-CM-PANI(Zn) catalyst was synthesized using the two nitrogen-precursor (cyanamide and PANI) approach, developed previously by LANL[2]. ZnCl2 was mixed with nitrogen precursors and heat-treated at 1000 ºC to ensure complete removal of Zn. The resulting CM-PANI-Fe(Zn) catalyst had much higher surface area than the catalyst obtained without Zn under the same conditions. The half-wave potential (E½ ) for CM-PANI-Fe(Zn) in RDE testing in acidic electrolyte, 0.79 V vs. RHE, was similar to that obtained with Zn-free CM-PANI-Fe heat-treated at 900 ºC (optimal heat-treatment temperature for the Zn-free system), but by 0.16 V higher than E½ measured with the Zn-free catalyst heat-treated at 1000 ºC (Figure 1). While no immediate increase in the activity can be demonstrated with CM-PANI-Fe(Zn), this catalyst promises to have much improved stability thanks to being treated at a much higher temperature. Electrochemical and fuel cell testing of the Zn-derived catalyst, focusing in particular on the durability, is underway, as is the catalyst structure optimization. The results will be present at the meeting.

Highly Stable Hierarchical Polybenzimidazole (PBI) Grafted Graphene/Nanographene Hybrids As Catalyst Supports for Polymer Electrolyte Membrane Fuel Cells

Graphene synthesized from the exfoliation of graphite has a great potential in polymer electrolyte membrane fuel cell (PEMFC) applications.[1] The highly graphitic structure composed of the conjugated carbons endows graphene with extremely high electric conductivity and chemical/electrochemical stability. Improved stability is required for PEMFC catalyst support materials as the stability plays a critical role in determining the overall durability of PEMFC systems. While graphene is an attractive material, there are three major barriers when using graphene-supported Pt-based catalysts in PEMFCs: 1) the lack of bonding sites for catalyst landing on the basal plane of graphene causes the migration/aggregations of Pt nanoparticles when subjected to harsh accelerated stress tests (ASTs), 2) the highly hydrophobic surface of graphene is difficult to wet when mixed with the Nafion ionomer particles, leading to a poor catalyst/ionomer interface, 3) 2D graphene sheets tends to restack back to graphite structure through π-π interactions, which can severely block the O2 diffusion and retard the catalytic reactions, in particular when PEMFCs are operated at high current density (>1.5 A/cm2),and 4) the exfoliation of natural graphite using wet chemistry method usually yield graphene that contains some defects and oxygenated functional groups, which can de-stabilizes its conjugated electronic structure which negatively affects electronic conductivity and stability. Furthermore, when subjected to harsh potential cycling (e.g. 1.0-1.5 V; potentials which can be observed during start-up/shut-down or local fuel starvation), these defect sites are vulnerable to carbon corrosion. To overcome these challenges, we use a novel approach to make the 2D graphene sheets into 3D composite materials with many channels and pores to facilitate the facile mass transport by developing the highly stable hierarchical polybenzimidazole (PBI) -grafted graphene hybrids supported Pt catalysts for PEMFCs. PBI- functionalization is found to homogenize the chemical environment of graphene surface, resulting in a uniform dispersion of Pt nanoparticles that exposes more active sites for electro-catalytic reactions. In order to construct appropriate pore structures in the catalyst layers, spacers were introduced using graphitized carbon materials or metal oxides. The surface charge was imposed on the surfaces of these spacer-particles as opposed to PBI-graphene, so that the columbic attraction forces drive them to anchor onto graphene sheets. As a result, the secondary pore volume (characterized by mercury porosimetry) significantly increases, leading to the improved mass transport of reactants (H2 and O2) and water, and consequently an improvement in the PEMFCs performance at high current density (i.e. 2.0 A/cm2). Additionally, we prepared graphene nanoplatelet with smaller dimensions as the catalyst supports, which leads to extra voltage gains at the high current density. Covalent grafting polymers onto graphene sheets containing semi-flexible backbones on graphene defects can help to re-build the conjugated carbons and de-localize the electron, as well seal the dangling bond resulting from graphene synthesis. The PEMFC durability studies carried out by our research group has shown significant improvement on support stability when they were cycled between 1.0 V to 1.5 V for 5000 cycles compared to traditional carbon support materials,[RB1]during which the mass activity is only decreased by 47% for Pt/PBI-graphene and 25% for Pt/PBI-nanographene. The reported results are very close to DOE 2020 targets on catalyst support stability [2]. In addition, these materials show improved Pt stability. Strengthened interaction between functional groups and Pt particles, as characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) greatly improves the catalyst stability. Our developed PBI-graphene supported Pt demonstrated a 27% decrease in mass activity and 15% loss of ECSA after 10,000 cycles between 0.6 V and 1.0 V. This exceeds the DOE 2020 targets for automotive PEM fuel cell electro-catalysts.[2] The unique advantages of the hierarchical PBI-functionalized graphene/nanographene hybrids demonstrates the potential for these materials to be the next generation of catalyst supports for PEMFCs. [1]. Geim, A. K.; Novoselov, K. S. Nat. Mater. 2007, 6, 183 [2]. U.S. DRIVE FuelCell Tech Team Cell Component Accelerated Stress Test Protocols for PEM Fuel Cells (2013)

The Operation of Polymer Electrolyte Membrane Fuel Cell using Hydrogen Produced from the Combined Methanol Reforming Process

A combined system with PEMFC and reformer is introduced and optimized for the real use of this kind of system in the future. The hydrogen source to operate the PEMFC system is methanol, which needs two parts of methanol reforming reaction and preferential oxidation (PROX) for the hydrogen fuel process in the combined operation PEMFC system. With the optimized methanol steam reforming condition, we tested PROX reactions in various operation temperature from 170 to 270 ℃ to investigate CO concentration data in the reformed gases. Using these different CO concentration, PEMFC performances are achieved at the combined system. Pt/C and Ru promoted Pt/C were catalysts were used for the anode to compare the stability in CO contained gases. The alloy catalyst of PtRu/C shows higher performance and better resistance to CO than the Pt/C at even high CO amount of 200 ppm, indicating a promotion not only to the activity but also to the CO tolerance. Furthermore, in a system point of view, there is a fluctuation in the PEMFC operation due to the unstable fuel supply. Therefore, we also modified the methanol reforming by a scaled up reactor and pressurization to produce steady operation of PEMFC. The optimized system with the methanol reformer and PEMFC shows a stable performance for a long time, which is providing a valuable data for the PEMFC commercialization. Keywords: Methanol reforming, Preferential oxidation (PROX), Polymer Electrolyte Membrane Fuel Cell (PEMFC), Alloy catalyst

Examination of the grid‐connected polymer electrolyte membrane fuel cell's electrical behaviour and control

Fuel cells (FCs) are considered as one of the most promising sources of electrical energy that can meet environmental constraints. One of the important steps to ensure clean energy is seamless power transfer from the FC to the grid. In this study, the behaviour of the FC under AC load and grid connection of FC system is simulated. Required interface for FCs' grid connection is performed with PSCAD software. For this purpose, polymer electrolyte membrane (PEM) FC model is developed in PSCAD software. Power converter units are designed to supply DC and AC loads. Control structures are developed for DC–DC converter and DC–AC inverter models in PSCAD. Power conditioning units are separately controlled by proportional–integral controller. The electrical behaviour and control of FCs are investigated and simulated using PSCAD software. Then a developed PEM FC system model is tested for AC load conditions. The PEM FC system is connected to grid and the behaviours of grid connected FC system are examined.

Online implementation of SVM based fault diagnosis strategy for PEMFC systems

In this paper, the topic of online diagnosis for Polymer Electrolyte Membrane Fuel Cell (PEMFC) systems is addressed. In the diagnosis approach, individual cell voltages are used as the variables for diagnosis. The pattern classification tool Support Vector Machine (SVM) combined with designed diagnosis rule is used to achieve fault detection and isolation (FDI). A highly-compacted embedded system of the System in Package (SiP) type is designed and fabricated to monitor individual cell voltages and to perform the diagnosis algorithms. For validation, the diagnosis approach is implemented online on PEMFC experimental platform. Four concerned faults can be detected and isolated in real-time.

A simplified PEM fuel cell model for building cogeneration applications

A simplified model of a polymer electrolyte membrane (PEM) fuel cell has been suggested for simulating packaged commercial fuel cell systems. PEM fuel cell systems are used in building cogeneration applications because of their high efficiency, low transmission loss and pollution, flexible scalability, and low noise. In conventional cogeneration applications, optimization techniques are utilized to size a system and determine proper operational strategies using simulations. To evaluate the performance of a building cogeneration system, a fuel cell model should be concise but accurate to allow its implementation in a whole-building simulation program. Some existing models are appropriate for building applications, but they have some limitations in modeling when a commercial packaged fuel cell system is used. To overcome these problems, a simplified fuel cell model is suggested for commercial packaged fuel cells by adding some new variables and validating through experimental and published data. This model is relatively simple compared to other models but can be easily utilized in some limited cases with performance predictions.

Fault Tolerant Control Strategy applied to PEMFC water management

In this paper, a Fault Tolerant Control Strategy (FTCS) dedicated to PEMFC (Polymer Electrolyte Membrane Fuel Cell) water management is implemented and validated online on a real PEMFC system. Thanks to coupling a Fault Detection and Isolation (FDI), an adjustable controller and a reconfiguration mechanism, FTCS allows addressing the important challenge of Fuel Cell (FC) reliability improvement. Only few works have already been conducted on FTCS applied to FC actuators faults, and none of them on FC water management faults. In this work, a neural-based diagnosis tool is computed online as FDI component and is coupled to a self-tuning PID controller. This diagnosis tool shows low computational time and high detection performance. The self-tuning PID controller shows robustness against noise measurements and model uncertainties. Its low computational cost makes it a suitable control method for real-time FTCS. Performed on a PEMFC system, the FTCS shows promising results on fault diagnosis and performance recovery.

Power Control for Efficient Operation of a PEM Fuel Cell System by Nonlinear Model Predictive Control

Efficiency of polymer electrolyte membrane (PEM) fuel cells depends directly on anode and cathode gas pressures, and stack temperature. For an efficient chemical reaction and a safe operation for both stationary and dynamic loads all values must fall within specific ranges. This paper deals with realtime nonlinear model predictive control (NMPC) of electrical power for a PEM fuel cell system. The NMPC is split into three nonlinear optimization problems to calculate the optimal stack current and the supply of anode and cathode with hydrogen and oxygen. For real-time application the predictive control algorithm is matched to the sampling time of the system. This NMPC handles all kinds of dynamic load changes, while maximizing power efficiency without a steady state error. Modeling of relevant anode and cathode site fuel cell peripherals is shown. Experimental results on a test bench with a 4.4kW PEM fuel cell are presented.

Optimal Feedback Linearization Control of PEM Fuel Cell

Abstract—This paper presents a new method to design nonlinear feedback linearization controller for PEMFCs (Polymer Electrolyte Membrane Fuel Cells). A nonlinear controller is designed based on nonlinear model to prolong the stack life of PEMFCs. Since it is known that large deviations between hydrogen and oxygen partial pressures can cause severe membrane damage in the fuel cell, feedback linearization is applied to the PEMFC system so that the deviation can be kept as small as possible during disturbances or load variations. To obtain an accurate feedback linearization controller, tuning the linear parameters are always important. So in proposed study NSGA (Non-Dominated Sorting Genetic Algorithm)-II method was used to tune the designed controller in aim to decrease the controller tracking error. The simulation result showed that the proposed method tuned the controller efficiently.

고분자 전해질 연료전지용 막가습기의 상대습도 추정을 위한 소프트센서 개발

It is important to accurately measure and control the relative humidity of humidified gas entering a PEM (polymer electrolyte membrane) fuel cell stack because the level of humidification strongly affects the performance and durability of the stack. Humidity measurement devices can be used to directly measure the relative humidity, but they cost much to be equipped and occupy spaces in a fuel cell system. We present soft sensors for predicting the relative humidity without actual humidity measuring devices. By combining FIR (finite impulse response) model with PLS (partial least square) and SVM (support vector machine) regression models, DPLS (dynamic PLS) and DSVM (dynamic SVM) soft sensors were developed to correctly estimate the relative humidity of humidified gases exiting a planar-type membrane humidifier. The DSVM soft sensor showed a better prediction performance than the DPLS one because it is able to capture nonlinear correlations between the relative humidity and the input data of the soft sensors. Without actual humidity sensors, the soft sensors presented in this work can be used to monitor and control the humidity in operation of PEM fuel cell systems.

선박 추진용 25kW급 고분자전해질 연료전지 시스템 개발

A 25kW-class polymer electrolyte membrane (PEM) fuel cell system has been developed for the propulsion of a leisure boat. The fuel cell system was designed to satisfy various performance requirements, such as resistance to shock, stability under rolling and pitching oscillations, and durability under salinity condition, for its marine applications. Then, the major components including a 30kW-class PEM fuel cell stack, a DC-DC converter, a seawater cooling system, secondary battery packs, and balance of plants were developed for the fuel cell system. The PEM fuel cell stack employs a unique design structure called an anodic cascade-type stack design in which the anodic cells are divided into several blocks to maximize the fuel utilization without hydrogen recirculation devices. The performance evaluation results showed that the stack generated a maximum power of 31.0kW while maintaining a higher fuel utilization of 99.5% and an electrical efficiency of 56.1%. Combining the 30-kW stack with other components, the 25kW-class fuel cell system boat was fabricated for a leisure. As a result of testing, the fuel cell system reached an electrical efficiency of 48.0% at the maximum power of 25.6kW with stable operability. In the near future, two PEM fuel cell systems will be installed in a 20-m long leisure boat to supply electrical power up to 50kW for propelling the boat and for powering the auxiliary equipments.

Real time control of air feed system in a PEM fuel cell by means of an adaptive neural-network

This paper proposes an adaptive B-spline neurocontroller (B-SNN) for the optimal air supply into a Polymer Electrolyte Membrane Fuel Cell (PEMFC). The B-SNN is proposed due to its simple structure, adaptability, and robustness, taking into account the PEMFC's nonlinearities. Furthermore, B-SNN has the capabilities of on-line learning and real time operation. The proposed neurocontroller is tested on a PEMFC hardware-in-loop (HIL) emulator. The FC emulator is based on a detailed nonlinear simulator taken from the open research. Real time results of the PEMFC system emulator and the neurocontroller obtained by the hardware-in-the-loop strategy are exhibited.

Designing Controller for Joined Dynamic Nonlinear PEMFC and Buck Converter System

Designing controller for a class of dynamical nonlinear model for Polymer Electrolyte Membrane Fuel Cell (PEMFC) is discussed in this paper inwhich the PEMFC system is used for powering a Notebook PC (Processing Computer). The power requirement of a Notebook PC varies significantly under different operational conditions. The proposed feedback controller is applied for the buck dc/dc converter to stabilize the load voltage at a desirable level under various operational conditions. The simulation results show the promising performance of the proposed controller at the different operating conditions. DOI: http://dx.doi.org/10.11591/ijpeds.v4i2.5195