Transient power characteristic measurement of a proton exchange membrane fuel cell generator

An experimental study on the transient power characteristics of a fuel cell generator has been conducted. The generator is hybridized by a proton exchange membrane (PEM) as the main power source and a lithium-ion battery as the secondary power source. power-conditioning module consisting of a main bidirectional converter and an auxiliary converter has been designed to manage the hybrid power of the generator that copes with fast dynamics of variable loads. Sensors embedded in the generator have measured the electrical properties dynamically. It was found that the present power-conditioning scheme has well controlled the power flow between the fuel cell stack and the battery by regulating the power flow from or to the battery. In addition, the thermal management system using pulse width modulation (PWM) schemes could limit the operation temperature of the fuel cell generator in a designed range. Furthermore, the dynamics of electrical efficiency of the generator are found to be parallel with those of the net system power. Finally, the stability and reliability of the fuel cell generator is proven by the rational dynamic behaviors of thermal and electrical properties for over 30-h demonstration.     

Weighted fusion control for proton exchange membrane fuel cell system

Oxygen excess ratio (OER) is closely correlated with the power generation efficiency and dynamic performance of proton exchange membrane fuel cell (PEMFC) system. As OER changes with varying load, it is prone to oxygen starvation and slow response to OER reference value, and great challenges to OER control technology are brought. To this end, a dual closed-loop weighted fusion control for PEMFC system is proposed. The outer loop is utilized to obtain the optimal OER reference value, and the inner loop is utilized to track the OER reference value. This inner loop combines the merits of active disturbance rejection control (ADRC) algorithm and fuzzy self-tuned PID (FSTPID) method. Simulation results reveal that the proposed approach is superior to the other three methods in reducing the overshoot, settling time and avoiding oxygen starvation issues, and also in improving several key performance indices, such as integrated absolute error, settling time, etc.     

Multivariable robust control of a proton exchange membrane fuel cell system

This paper applies multivariable robust control strategies to a proton exchange membrane fuel cell (PEMFC) system. From the system point of view, a PEMFC can be modeled as a two-input-two-output system, where the inputs are air and hydrogen flow rates and the outputs are cell voltage and current. By fixing the output resistance, we aimed to control the cell voltage output by regulating the air and hydrogen flow rates. Due to the nonlinear characteristics of this system, multivariable robust controllers were designed to provide robust performance and to reduce the hydrogen consumption of this system. The study was carried out in three parts. Firstly, the PEMFC system was modeled as multivariable transfer function matrices using identification techniques, with the un-modeled dynamics treated as system uncertainties and disturbances. Secondly, robust control algorithms were utilized to design multivariable H_∞ controllers to deal with system uncertainty and performance requirements. Finally, the designed robust controllers were implemented to control the air and hydrogen flow rates. From the experimental results, multivariable robust control is shown to provide steady output responses and significantly reduce hydrogen consumption.     

Development of a proton exchange membrane fuel cell cogeneration system

A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.     

Dynamic modeling and simulation of air-breathing proton exchange membrane fuel cell

Small fuel cells have shown excellent potential as alternative energy sources for portable applications. One of the most promising fuel cell technologies for portable applications is air-breathing fuel cells. In this paper, a dynamic model of an air-breathing PEM fuel cell (AB-PEMFC) system is presented. The analytical modeling and simulation of the air-breathing PEM fuel cell system are verified using Matlab, Simulink and SimPowerSystems Blockset. To show the effectiveness of the proposed AB-PEMFC model, two case studies are carried out using the Matlab software package. In the first case study, the dynamic behavior of the proposed AB-PEMFC system is compared with that of a planar air-breathing PEM fuel cell model. In the second case study, the validation of the air-breathing PEM fuel cell-based power source is carried out for the portable application. Test results show that the proposed AB-PEMFC system can be considered as a viable alternative energy sources for portable applications.     

Dynamic modeling of a high-temperature proton exchange membrane fuel cell with a fuel processor

A dynamic model of a high-temperature proton exchange membrane fuel cell with a fuel processor is developed in this study. In the model, a fuel processing system, a fuel cell stack, and an exhaust gas burner are modeled and integrated. The model can predict the characteristics of the overall system and each component at the steady and transient states. Specifically, a unit fuel cell model is discretized in a simplified quasi-three-dimensional geometry; therefore, the model can rapidly predict the distribution of fuel cell characteristics. Various operating conditions such as the steam-to-carbon ratio, oxygen-to-carbon ratio, and autothermal reforming inlet temperature are varied and investigated in this study. In addition, the dynamic characteristics exhibited during the transient state are investigated, and an efficiency controller is developed and implemented in the model to maintain the electrical efficiency. The simulation results demonstrate that the steam-to-carbon ratio and the oxygen-to-carbon ratio affect the electrical and system efficiency and that controlling the fuel flow rate maintains the electrical efficiency in the transient state. The model may be a useful tool for investigating the characteristics of the overall system as well as for developing optimal control strategies for enhancing the system performance.     

Thermodynamic modeling and exergy analysis of proton exchange membrane fuel cell power system

The proton exchange membrane (PEM) fuel cell (PEMFC) is equipped with a series of auxiliary components which consume considerable amount of energy. It is necessary to investigate the design and operation of the PEMFC power system for better system performance. In this study, a typical PEMFC power system is developed, and a thermodynamic model of the system is established. Simulation is carried out, and the power distribution of each auxiliary component in the system, the net power and power efficiency of the system are obtained. This power system uses cooling water for preheating inlet gases, and its energy-saving effect is also verified by the simulation. On this basis, the exergy analysis is applied on the system, and the indexes of the system exergy loss, exergy efficiency and ecological function are proposed to evaluate the system performance. The results show that fuel cell stack and heat exchanger are the two components that cause the most exergy loss. Furthermore, the system performance under various stack inlet temperatures and current densities is also analyzed. It is found that the net power, energy efficiency and exergy efficiency of the system reach the maximum when the stack inlet temperature is about 348.15 K. The ecological function is maintained at a high level when the stack inlet temperature is around 338.15 K. Lower current density increases the system ecological function and the power and exergy efficiencies, and also helps decrease the system exergy loss, but it decreases the system net power.     

Modeling and simulation of a proton exchange membrane fuel cell using computational fluid dynamics

An isothermal, three dimensional, single phase model was presented to evaluate a proton exchange membrane fuel cell (PEMFC) with serpentine flow. The mass, momentum and electrochemical equations were solved simultaneously for the steady state condition using computational fluid dynamics (CFD) software based on the finite element method. The model considered reactions as mass source/sink terms, and electron transport in the catalyst layers and GDLs. To validate the model, the numerical results were compared to the experimental data collected from the fabricated membrane electrode assemblies. The exchange current density parameter of the catalysts was fitted by the model to calibrate the results. The model showed good agreement with experimental data and predicted a higher current density for the catalyst with a higher surface area and Pt content. The oxygen, hydrogen and water mass fraction distribution, velocity magnitude and pressure distribution were estimated by the model. Moreover, the effect of pressure and temperature, as two important operating conditions, on the current density was predicted by the validated model.     

Design of proton exchange membrane fuel cell grid-connected system based on resonant current controller

Because of its high efficiency, low pollution and good stability, proton exchange membrane fuel cell (PEMFC) is considered as one of the most promising technologies for a wide range of applications, such as distributed power generation, transportation, portable power source and automobile. In a PEMFC grid-connected system, the proportion integration (PI) regulator can achieve zero error for the dc components in the rotating frame, but cannot achieve zero error for the ac components in the rotating frame. Hence, the PEMFC grid-connected system will produce a large number of harmonics. In order to overcome this shortcoming, a proportion integration resonant (PIR) controller is utilized to realize zero magnitude error and selective disturbance rejection. Instead of the PIR controller, a vector proportion integration (VPI) controller is designed to quickly and accurately regulate current which achieve zero both amplitude and phase frequency response at the resonant frequency simultaneously. In this paper, the PEMFC grid-connected system based on PIR and VPI controllers are developed according to the operating characteristics of a PEMFC generation system, then analyze and compare the performance of compensation harmonics between them. The total harmonic distortion (THD) of grid-connected voltage and current are measured by means of the criterion of IEEE Std1547-2003. This proposed grid-connected method will provide a novel approach for the design of advanced PEMFC grid-connected control system.     

A critical survey of proton exchange membrane fuel cell system control: Summaries,advances, and perspectives

Proton exchange membrane fuel cell (PEMFC) is a promising future power source, which uses hydrogen energy to generate electricity with the byproduct of water. In general, PEMFC includes several strongly coupled subsystems with high nonlinearity and complex dynamic processes. Therefore, proper control strategies are crucial for a reliable and effective PEMFC operation. This paper aims to carry out a comprehensive and systematic overview of state-of-the-art PEMFC control strategies. Based on a thorough investigation of 180 literatures, these control strategies are classified into nine main categories, including proportional integral derivative (PID) control, adaptive control (APC), fuzzy logic control (FLC), robust control, observer-based control, model predictive control (MPC), fault tolerant control (FTC), optimal control and artificial intelligence control. Furthermore, a comprehensive evaluation and detailed summary of their control deigns, objectives, performance, applications, advantages/disadvantages, complexity, robustness and accuracy are conducted thoroughly. Finally, five valuable and insightful perspectives/recommendations are proposed for future research.     

Cross-linked PEEK-WC proton exchange membrane for fuel cell

The low cost proton exchange membrane was prepared by cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC). The prepared cross-linked membrane became insoluble in water, and exhibited high proton conductivity, 2.9 × 10⁻² S/cm at room temperature. The proton conductivity was comparable with that of Nafion^® 117 membrane (6.2 × 10⁻² S/cm). The methanol permeability of the cross-linked membrane was 1.6 × 10⁻⁷ cm²/s, much lower than that of Nafion^® 117 membrane.     

Dynamic modeling of a proton exchange membrane fuel cell system with a shell-and-tube gas-to-gas membrane humidifier

The proton exchange membrane fuel cell (PEMFC) system with a shell-and-tube gas-to-gas membrane humidifier is considered to be a promising PEMFC system because of its energy-efficient operation. However, because the relative humidity of the dry air flowing into the stack depends on the stack exhaust air, this system can be unstable during transients. To investigate the dynamic behavior of the PEMFC system, a system model composed of a lumped dynamic model of an air blower, a two-dimensional dynamic model of a shell-and-tube gas-to-gas membrane humidifier, and a one-dimensional dynamic model of a PEMFC system is developed. Because the water management during transient of the PEMFC system is one of the key challenges, the system model is simulated at the step change of current. The variations in the PEMFC system characteristics are captured. To confirm the superiority of the system model, it is compared with the PEMFC component model during transients.     

Control of a heat-integrated proton exchange membrane fuel cell system with methanol reforming

This work presents a novel heat-integrated fuel cell stack system with methanol reforming. Its configuration is composed of fuel processing units (FPUs), proton exchange membrane (PEM) fuel cell stack, and heat exchangers (HEXs). Well mixed methanol and oxygen flows in contact with countercurrent flowing water dominates the production of hydrogen at the exit of FPUs and influences the stack temperature. The heat exchange connections can enhance the utilization of energy of FPUs. To ensure the stable steady-state operation, the model-free fuzzy incremental control scheme within the multi-loop feedback control framework is developed. Finally, the proposed system integration and control configuration are verified by closed-loop simulations.     

Comb-shaped sulfonated poly(aryl ether sulfone) proton exchange membrane for fuel cell applications

Structure design is the primary strategy to acquire suitable ionomers for preparing proton exchange membranes (PEMs) with excellent performance. A series of comb-shaped sulfonated fluorinated poly(aryl ether sulfone) (SPFAES) membranes are prepared from sulfonated fluorinated poly(aryl ether sulfone) polymer (SPFAE) and sulfonated poly(aryl ether sulfone) oligomer (SPAES-Oligomer). Chemical structures of the comb-shaped membranes are verified by ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectra. The comb-shaped SPFAES membranes display more continuous hydrophilic domains for ion transfer, because the abundant cations and flexible side-chains structure possess higher mobility and hydrophilicity, which show significantly improved proton conductivity, physicochemical stability, mechanical property compared to the linear SPFAE membranes. In a H₂/O₂ single-cell test, the SPFAES-1.77 membrane achieves a higher power density of 699.3 mW/cm² in comparison with Nafion® 112 (618.0 mW/cm²) at 80 °C and 100% relative humidity. This work offers a promising example for the synthesis of highly branched polymers with flexible comb-shaped side chains for high-performance PEMs.     

SnO2 nanoparticles dispersed carboxylated Poly(arylene ether sulfones) nanocomposites for proton exchange membrane fuel cell (PEMFC) applications

The new poly (arylene ether sulfone) (CPAEs) polymer, and carboxylated through simple Thiol Ene reaction, is characterized by FTIR, ¹H NMR. The SnO₂ nanoparticles are synthesized via alkaline and template free, one-pot hydrothermal method and characterized using HRTEM analysis. SnO₂ nanoparticles in dispersed CPAEs polymer is synthesized and examined by PXRD, SEM and TGA analyses. Further, the typical properties of bare CPAEs and 1%, 2% and 3% SnO₂ NPs of dispersed CPAEs nanocomposite membranes such as water uptake, swelling ratio, ion exchange capacity, proton conductivity and oxidative stability are evaluated. The PXRD pattern suggests the successful formation of amorphous natured CPAEs polymer and tetragonal rutile structured in SnO₂ NPs. It is observed that the SEM images indicate SnO₂ NPs, bare CPAEs polymers as spherical and form wavelike morphology. It is also noted that the HR-TEM image has identified SnO₂ NPs as non-uniform in size with an average particle size of 4 nm. 3% SnO₂ NPs loaded with CPAEs nanocomposite membrane exhibits an IEC value at 0.78 mmol/g-1 and a proton conductivity value of around 1.49 × 10^?3 S/cm^?1 at 100 °C. It shows excellent oxidative stability with a value of 12.3% degradation after being exposed to Fenton reagent at 68 °C for 8 h.     

Model-based decoupling control for the thermal management system of proton exchange membrane fuel cells

As one of the most promising sustainable energy technologies available today, proton exchange membrane fuel cell (PEMFC) engines are becoming more and more popular in various applications, especially in transportation vehicles. However, the complexity and the severity of the vehicle operating conditions present challenges to control the temperature distribution in single cells and stack, which is an important factor influencing the performance and durability of PEMFC engines. It has been found that regulating the input and output coolant water temperature can improve the temperature distribution. Therefore, the control objective in this paper is regulating the input and output temperature of coolant water at the same time. Firstly, a coupled model of the thermal management system is established based on the physical structure of PEMFC engines. Then, in order to realize the simultaneous control of the inlet and outlet cooling water temperature of the PEMFC stack, a decoupling controller is proposed and its closed-loop stability is proved. Finally, based on the actual PEMFC engine platform, the effectiveness, accuracy and reliability of the proposed decoupling controller are tested. The experimental results show that with the proposed decoupling controller, the inlet and outlet temperatures of the PEMFC stack cooling water can be accurately controlled on-line. The temperature error range is less than 0.2 °C even under the dynamic current load conditions.     

Convergence criteria establishment for 3D simulation of proton exchange membrane fuel cell

A validated 3 dimensional (3D) computational fluid dynamics model of a single cell proton exchange membrane fuel cell (PEMFC) was used for investigating convergence criteria. The simulation study was carried out using the commercial PEMFC simulation module built in to ANSYS FLUENT 12.1 software package and compared with published experimental data. Convergence data up to 19,000 iterations were collected in order to establish expectations for convergence errors and differences in convergence rates for different boundary conditions. Species mass fluxes and current density were used to perform a dual verification of experimentally verifiable simulation predictions. The results of the simulation showed that convergence trends were consistent for different boundary conditions and that the solution trends asymptotically to a final value with species mass flux errors approaching to constant values. The data were used to establish convergence criteria for future 3D PEMFC simulations where residual monitoring alone is insufficient to ensure convergence.     

Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

The proton exchange membrane based on polyetheretherketone was prepared via two steps of cross-linking. The properties of the double cross-linked membrane (water uptake, proton conductivity, methanol permeability and thermal stability) have been investigated for fuel cell applications. The prepared membrane exhibited relatively high proton conductivity, 3.2 × 10⁻² S cm⁻¹ at room temperature and 5.8 × 10⁻² S cm⁻¹ at 80 °C. The second cross-linking significantly decreased the water uptake of the membrane. The performance of direct methanol fuel cell was slightly improved as compared to Nafion^® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell, especially for the direct methanol fuel cell due to its low methanol permeability and high stability in a methanol solution.     

Thermodynamic study of integrated proton exchange membrane fuel cell with vapour adsorption refrigeration system

With the rising usage of fossil fuels, there is an urgent need to develop new technologies specifically based on renewable energy sources to power the vehicles running on fuel. A fuel cell is an electrochemical cell that is used to convert the chemical energy of a fuel directly to electric power. Fuels cells possess advantages such as smaller size, high efficiency, silent operation, etc. However, there can be significant variations in the size and power output of the fuel cells depending upon the application. The focus of this paper is to estimate the performance of an integrated system comprising of Polymer Exchange Membrane Fuel cell (PEMFC) and vapour adsorption refrigeration system to produce electric output and cooling effect simultaneously. The adsorption system in this study is based on activated carbon and methanol combination. The effect of operating parameters such as the operating temperature, current density and evaporator temperature on the energy and exergy efficiency of the system is presented. The study shows a remarkable improvement in the performance of the integrated system compared to PEMFC alone. The results show that the system energy and exergy efficiency decrease as the current density value increases. Maximum system energy and exergy efficiency of 63.01% and 29.88% are achieved. In addition, a maximum energy efficiency of 65.39% was reported at an evaporator temperature of 5 °C and a current density of 0.8 A/cm².     

Coolant circuit modeling and temperature fuzzy control of proton exchange membrane fuel cells

Effective temperature management is necessary for the safe and efficient operation of proton exchange membrane fuel cells (PEMFC). Generally circulating coolant can be applied in removing the excess heat of the PEMFC whose electrical power exceeds 5 kW. So a coolant circuit modeling method and a temperature fuzzy control strategy are presented in the paper in order to keep the PEMFC within the ideal operation temperature range. Firstly, a coolant circuit mathematical model is developed, which includes a PEMFC thermal model, a water reservoir model, a water pump model, a bypass valve model, a heat exchanger model and a PEMFC electrochemical model. Secondly, the incremental fuzzy control with integrator technique is designed according to the established model and control experience rule. And the PEMFC temperature and circulating coolant inlet temperature are controlled by regulating the circulating coolant flux and bypass valve factor respectively. Finally, the established model and fuzzy controllers are simulated and analyzed in Matlab software, and the simulation results demonstrate that the incremental fuzzy controller with integrator can effectively control the PEMFC temperature and the inlet coolant temperature within their objective working ranges respectively. In addition, the modeling and control process are very concise, and they can be easily applied in various power classes PEMFC temperature control in real-time.