Methods to Improve Response Time in Fuel Cell Systems

This paper outlines a semi-empirical model to account for the transient response of Polymer Electrolyte Membrane Fuel Cells (PEMFC) during load changes. In this work, we investigated the voltage undershoots of the PEMFC system with a current step-up given as the input. The dynamic response of PEMFC during stepwise load changes is a vital factor that indicates cell performance. We present a model based on mass balance equations, various transport phenomena, and experimental conditions for these voltage undershoots. This models response highlights the impact of reactant starvation inside the fuel cell stack during step increase in current. A single fuel cell is divided into two domains to analyze the availability of reactant gases. The model can anticipate the impact of different operating conditions on the magnitude of voltage undershoots. Validation of the model with experimental data resulted in a maximum relative error of 4.59%, with the goodness of fit in the range of 0.96 to 0.99, making the model statistically significant.

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Introduction Fuel cell technology is a harbinger of the future for generating electricity due to their high efficiency and low emissions achieved through the direct conversion of chemical energy into electrical energy without combustion. Methods To optimize the design and performance, a fuel cell model is essential to predict its behaviour in different conditions. This technical note presents a novel physics-based approach, the Youngs Double-slit Experiment Optimizer (YDEO), for identifying parameters in Proton Exchange Membrane Fuel Cells. A performance metric is established by formulating an objective function that relies on the summation of squared errors between experimental and estimated values. Results and discussion The effectiveness of this approach is evaluated through the analysis of four benchmark test cases: Horizon 500 W, BCS500 W, NedstackPS6, and 250 W. The corresponding objective function values for these test cases are 0.011243, 2.065557, 0.011698, and 5.250849, respectively. The simulation results demonstrate the efficacy of the proposed YDEO algorithm when compare... Read More

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Fuel cell vehicles (FCVs) represent a pivotal advancement in the evolution of future automobile technologies. This paper introduces a comprehensive approach to enhancing the performance of automotive fuel cells, employing the Predictive Trip Distance Adaptive Equivalent Consumption Minimum Strategy (PTDA-ECMS) objective function for predictive analysis. By developing innovative alkaline electrolyte membranes, catalysts, and electrode materials, and implementing hybrid power system management strategies for fuel cell and battery integration, this study aims to extend fuel cell longevity, improve system efficiency, and reduce operational costs. Additionally, the use of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for electric catalyst evaluation signifies a methodical exploration into fuel cells with enhanced service life, reduced production expenses, and superior overall performance. Such advancements are anticipated to decrease the operational costs of electric vehicles, thereby increasing marketability and facilitating more sustainable human transportation solutions. This p... Read More

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In this paper, a meticulous modeling approach is proposed not only for a fuel cell stack itself but also for all auxiliary components that collectively form the fuel cell system. This comprehensive modeling approach encompasses a wide range of components, including, but not limited to, the hydrogen recirculation pump and the air compressor. Each component is thoroughly analyzed and modeled based on the detailed specifications provided by suppliers. This involves considering factors such as efficiency, operating parameters, response times, and interactions with other system elements. By integrating these detailed models, a holistic understanding of the entire fuel cell systems performance can be attained. Such an approach enables engineers and designers to simulate various operating scenarios, predict system behavior under different conditions, and optimize the system design for maximum efficiency and reliability. Moreover, it allows for informed decision-making throughout the systems development, deployment, and operational phases, ultimately leading to more robust and effective en... Read More

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To improve the fuel cell durability of the hydrogen Electric Multiple Units, this paper proposes a novel multi-stack fuel cell hybrid system energy management strategy in consideration of fuel cell degradation. The top layer of the method distributes the power of fuel cells and lithium batteries reasonably according to the Equivalent Consumption Minimization Strategy, and adjusts the fuel cell power through the feedback power regulation module. The bottom layer distributes the power of different stacks according to the degradation degree. The proposed layering method improves the durability of fuel cells by reducing the fuel cell degradation degree. The hardware-in-the-loop (HIL) experiments results show that, compared with the traditional equivalent hydrogen consumption minimum energy management strategy, the proposed method is effective in lowering the degradation degree and operating pressure of the fuel cell by 25.77% and 35.73% respectively.

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The adaptability of fuel cell vehicles in low-temperature environments remains challenging for their commercialization owing to the propensity of water within the fuel cell to freeze during a cold start, which impedes gas transmission and subsequent reactions. Consequently, the initial water content before cold start and the heat and water generated during this process are crucial for achieving a successful cold start. In this study, current- and voltage-controlled starting strategies are analyzed using a stack comprising 20 cells with an area of 285 cm 2 . Furthermore, key parameters related to shut down purging and cold start are optimized using starting time and reverse polarity cell count as optimization objectives. The optimal conditions for cold start include a current density of 0.5 A cm 2 , voltage of 0.45 V, purging time of 180 s, and stack temperature (during purging) of 60 C. Furthermore, the ambient temperature boundary is determined as 25 C30 C for a successful cold start without auxiliary heating in the stack.

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Activation is a crucial procedure to improve the performance of newly fabricated fuel cell stacks to meet the power requirements in actual application scenarios. However, traditional activation procedures generally last for several hours or even days, which greatly increases the cost and limits the production efficiency. In response to this problem, this paper proposes a rapid activation procedure composed of hydrogen pumping (HP) and limiting-current activation with limited air (LCA). The influence of current density for HP and air supply for LCA on activation effect is studied and the best operating conditions are determined. The importance of water supply to the cathode is highlighted during HP. The influence of air supply for LCA on activation effect is limited, which contributes to gas saving. According to the experiments conducted on a single cell and a 10-cell stack, only 40 min are needed with this combined procedure, which is much shorter than that of the traditional step-current activation. Furthermore, nearly 75% of hydrogen is saved due to the short activation time and th... Read More

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<title>Abstract</title> In fuel cells, disparities in individual cell performance can significantly impact various aspects of the overall system, including uneven energy output, accelerated aging, poor system stability, and decreased safety. Hence, enhancing the balance within fuel cells holds paramount importance. Accordingly, this study utilized Matlab and COMSOL to establish a 1D model of the fuel cell stack and a 3D model of individual cells for combined simulation. The aim was to analyze performance discrepancies between individual cells arising from flow distribution issues, investigate how flow rates affect individual cell performance, and ultimately, improve fuel utilization by optimizing individual cell flow channel dimensions. This optimization aimed to address performance deficiencies caused by insufficient gas supply. The research findings indicate that pre-optimization and post-optimization of flow field dimensions, the performance of cells experiencing insufficient gas supply (at the lowest inlet flow rate) improved by 5.59%. Increasing the inlet flow rate enhances indi... Read More

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Energy Management Strategies for Fuel Cell Vehicles: A Comprehensive Review of the Latest Progress in Modeling, Strategies, and Future Prospects

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The startup performance is crucial to the high-efficient operation of the sustainable power generation system. Current literature usually focuses on catalysts and startup strategy to improve startup performance of the proton exchange membrane fuel cell, which ignores the gas foil bearings-rotor system that directly affects startup response. Therefore, in this paper, the effects of bump foil structure, coating, and nominal clearance on the startup response of the bearings-rotor system are first investigated experimentally. Multi-objectives optimization mathematical model considering simultaneously lower power consumption, takeoff speed, and vibration is presented based on grey relational analysis. The optimal bearings-rotor system with radial trisection bump foil, coating MoS2, and nominal clearance of 50 m is identified. Compared to average values, the power consumption of the optimal system is diminished by 27.2% while the takeoff speed and nonlinear vibration are reduced by 16.2% and 47.3%, respectively. These findings can be used to improve energy efficiency and startup performan... Read More

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<title>Abstract</title> The performance of fuel cells is influenced by many factors, among which operating temperature is crucial. Therefore, this study focuses on analyzing the performance of fuel cells at different temperatures and optimizing operational parameters at the optimum temperature condition to enhance the performance and lifespan of fuel cells. The research finds that the optimal temperature for fuel cells is 69.9C, with an efficient operating temperature range of 6080C, and the optimal flow rate range is 10001600 ml/min. The influence of back pressure on fuel cell performance becomes less significant when it exceeds 2.5 bar. Furthermore, this study utilizes a Gaussian process regression model to optimize the performance of fuel cells under different temperature, flow rate, and back pressure combinations. Regression analysis model predictions suggest that the optimum operating temperature is 71C, with an optimal back pressure range of 0.91.4 bar and a flow rate range of 13101600 ml/min.

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Dynamic performance of proton exchange membrane fuel cell (PEMFC) significantly influences the durability and reliability. This study experimentally investigates the transient response of PEMFC when starting with different load levels under various operating conditions. The results indicate that the dynamic behavior follows a "two-stage" response mode when starting with a low load. While starting with a high load, due to the flooding at the cathode, the voltage fluctuation during the starting process is larger and the starting time is longer, following a "three-stage" response mode. Increasing the cathode stoichiometry ratio obviously enhances the dynamic performance of PEMFC during startup. Increasing the anode stoichiometry ratio has minimal impact on the dynamic behavior when starting with a low load, whereas starting with a high load it results in longer response time and larger voltage fluctuation. As the load carried at startup increases, augmenting cathode inlet humidity consistently improves the dynamic response of the output voltage more effectively than increasing anode inl... Read More

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Controlling the relative humidity is crucial for improving fuel cell performance in self-humidifying fuel cells. In light of this, this study investigates the influence of humidity variation on Proton Exchange Membrane Fuel Cells (PEMFC) performance through single-cell testing and a two-dimensional two-phase model. In the experiment, different humidity conditions are achieved by adjusting the inlet air temperature, and the effect of relative humidity on cell performance is observed. The research findings indicate that as the relative humidity increases, the performance of the fuel cell gradually improves. Increasing humidity reduces voltage fluctuations, particularly at low flow rates, demonstrating more stable performance. Under different humidity conditions, when the inlet air flow rate exceeds a certain value, the voltage non-uniformity of the cell remains within 1, indicating insignificant voltage fluctuations, attributed to the effects of inlet air flow rate on performance improvement and alleviation of flooding phenomena. Analysis of the two-dimensional two-phase model reveals ... Read More

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The low-temperature cold start has become one of the leading technical bottlenecks limiting the large-scale commercial application of proton exchange membrane(PEM) fuel cells. This paper establishes the 1-D numerical model of the fuel cell stack to study the reactant gas, charge transfer, heat transfer, and water phase transition process. Then the critical parameters in the numerical model of the fuel cell stack are identified based on the cold start experiment data. The identification results show that the cold start model is consistent with the experimental results, and the model's output voltage and average temperature errors are under the acceptable range. Based on the numerical model, with the cold start time as the optimization objective and load current and initial membrane water content as the optimization variable, the cold start strategy is optimized under different ambient temperatures. The results show that the optimized current loading strategy can reduce the cold start time of the fuel cell stack and achieve a fast, successful cold start for 20 C and 25 C condition... Read More

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Improving the commercial fuel cell system efficiency is critical to reducing hydrogen consumption and improving the operational economy. This paper studies the power consumption pattern of the air supply subsystem, the most power-consuming auxiliary components, aiming to improve the system's efficiency. A method was proposed to get the extremum of the system net power by optimizing the oxygen excess ratio and cathode pressure. Mathematical models describing the fuel cell stack and air supply subsystem power characteristics were developed based on the mechanism analysis and estimation of unknown parameters. Then, a system net power model for energy efficiency optimization was developed. The operating conditions for optimal efficiency at a specific current density can be obtained by numerical calculation. To verify the method's effectiveness, a series of experiments were conducted, and the results show that the proposed method can maximize system net power output at various current density conditions. Compared with the conventional oxygen excess rate based one-dimensional optimization,... Read More

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The energy management system and thermal control of fuel cell in fuel cell vehicles plays a crucial role in ensuring their stable and efficient operation.This study presents a novel fuel cell powertrain energy management system control strategy considered the temperature fluctuation based on deep reinforcement learning.A comprehensive SIMULINK model, encompassing fuel cell cooling system and stack models, was constructed for the fuel cell, followed by simulation testing under various temperature scenarios.To validate the robustness and stability of the control system, the standard operating conditions -US06 were employed for experimental verification.The experimental results highlight the effectiveness of the designed fuel cell energy management system in achieving transient temperature stabilization.Additionally, the results revealed that stable operation temperatures correlate with reduced hydrogen consumption.Furthermore, it's noted that fuel cell hydrogen consumption displays substantial variation under uniform operating conditions at varying temperatures.This highlights the key ... Read More

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Recently, the development of heavy-duty fuel cell vehicles (HDFCVs) has received intense attention. Unlike the refuelling protocol of SAE J2601 for light-duty fuel cell vehicles, the SAE J2601-2 for HDFCVs does not propose a specific filling strategy but only specifies the limits that need to be observed for safety. Refuelling data for HDFCVs at hydrogen refuelling station (HRS) shows that refuelling parameters are often set conservatively, resulting in long refuelling time. To shorten the refuelling time, energy consumption and power demand of the cooling system, we establish a detailed three-stage pressure filling model to study the effects of pressure ramp rate (PRR), initial pressure, number of onboard tanks and precooling temperature on the filling time. Then, a three-stage temperature precooling method is proposed simultaneously, whose cooling energy and power of the heat exchanger are compared with the single-stage temperature precooling method. Research shows that three-stage and two-stage pressure filling can reduce the average pressure difference between the station-side an... Read More

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PEM fuel cells are encouraging energy conversion technologies that offer low emissions and high efficiency for various applications, auto motives in particular. In order to create flexible and adaptive models that accurately depict the complex electrochemical, transport, and thermodynamic processes within these systems, a parameterized technique for modelling PEM fuel cells is essential. This work focuses on investigating the profound impact of load and temperature variations on the steady-state behavior of PEM fuel cells. The parameterized approach is then employed to develop a dynamic model of PEM fuel cells. The dynamic model captures the intricate dynamics of the cell under varying load conditions, considering the transient behavior of the cell components and the interactions between the different physical phenomena.

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The gas flow channels inside unitized regenerative fuel cells display obvious effects on relevant parameter changing behaviors such as species concentration, electrical signal and thermal signal during mode switching. In previous study, detailed transportation behaviors inside a cell constructed with streamlined channels have not been investigated. In our present study, a two-dimensional, transient model coupling non-isothermal characteristics is employed to study the changing characteristics of the cell with typical streamlined channel and comparatively analyze the channel structure impacts on the working states inside the operating cell regions. The simulated results indicate that when turning the mode from electrolyzer to fuel cells, the changing response occupied time of each parameter is required more, compared with the stabilizing procedure after entering the electrolytic cell procedure. For different oxygen-side channels, when reducing the channel depth, the current density output is raised, and the needed time-span for the stabilizing the working state is reduced. The present... Read More

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Abstract This paper aims to achieve stable and reliable operation of the marine PEM fuel cell systems. To accomplish this, a dynamic model that incorporates the thermodynamic electric potential and the three irreversible voltage losses of the fuel cell was established and simulated using Matlab/Simulink software based on the steady-state model of the PEM fuel cell. Under certain ideal conditions, the dynamic response of the PEM fuel cell was simulated and analyzed concerning various environmental factors and internal parameters of the fuel cell stack. An input signal source was used as an applied load for this purpose. The simulations and analysis focused on examining the impact of each factor on the performance of the PEM fuel cell. Specifically, the dynamic response is investigated when the load signal undergoes a step change. In addition to enhancing the drawbacks of the conventional steady-state system model, which tends to be complex with redundant parameters and a large amount of data, the dynamic model also establishes a theoretical foundation for optimizing the performance of... Read More

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This article addresses the need for improved fuel cell performance in vehicles through comprehensive research, encompassing literature review, fuel cell modeling, data analysis, and power curve optimization. It begins by analyzing experimental data from fuel cell buses to calibrate a dynamic model, ensuring its precision. This dynamic model accounts for internal heat and mass transfer within fuel cells, simulating water content levels under specific conditions. The study concludes by optimizing fuel cell power output curves, aiming for consistent average power. Four modes were researched (Real operation, Steady, Two-point-steady, and Triangular mode). Dryness is eliminated, and the time of flooding is decreased by 61.6% in the steady mode compared to the real operation. Furthermore, the water content during the operation of Two-point-steady and Triangular mode did not experience dryness or flooding. This research introduces a dynamic model for enhancing automotive fuel cell operation, holding significant implications for the transportation sector's adoption of fuel cell technology.

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Nowadays, there are already more and more proton exchange membrane fuel cell (PEMFC) buses demonstrated around the world. In order to improve the performance of automotive PEMFCs, it is necessary to understand the fuel cell working conditions and its degradation trend in real operation conditions. In this work, a study on statistical analysis of four hydrogen fuel cell buses is introduced. Fuel cell working conditions and energy management strategy of four fuel cell vehicles are extracted based on 550~870 hours fuel cell operating data, which mainly covers the rapid activation and linear decline stages of fuel cells. Long and short-term memory algorithm and linear regression algorithm are utilized in combination for performance degradation rate prediction. The relationship between fuel cell working conditions and degradation rates of four buses are analyzed. The results show that, load changing and start-stop operation are the two key operating conditions that accelerate the fuel cell aging. On the contrary, during activation period, frequent load changes are beneficial to increase f... Read More

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Fuel cells are now being employed as a source of energy and heat in industrial, transportation, and residential applications.This article presents the real-time implementations and functioning of the proton exchange membrane (PEM) fuel cells.The analysis had been carried out on PEM fuel cells to test the performance systematically and smoothly under transient operations.A change in the current and the resistance of the appliance had been considered for the load variations on PEMFC.This study examined the fuel cell system's efficiency and the time it taken to reach the steady-state without additional means using Artificial intelligence based back propagation network.The proposed analysis proves that the PEM fuel cells which are used for the installations with quickly changing load profiles can provide the improving the system's performance and efficiency.

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Fuel cell performances are directly linked to the operating conditions, which can fluctuate over time. The aim of this work is to introduce a fuel cell voltage prediction method based on the measured operating conditions while cycling a mission profile. The method is built and tested on analyzing the experimental results obtained during a test campaign while cycling a mission profile for 2030h. Four different configurations are illustrated and compared in this article, considering three different sets of parameters and two formulas.

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The cold start of fuel cells limits their wide application. Since the water produced by fuel cells takes up more space when it freezes, it may affect the internal structure of the stack, causing collapse and densification of the pores inside the catalytic layer. This paper mainly analyzes the influence of different startup strategies on the stack cold start, focusing on the change in the stack temperature and the ice volume fraction of the catalytic layer. When designing a startup strategy, it is important to focus not only on the optimization of the startup time, but also on the principle of minimizing the damage to the stack. A lumped parameter cold-start model was constructed, which was experimentally verified to have a maximum error of 8.9%. On this basis, a model predictive control (MPC) algorithm was used to control the starting current. The MPC cold-start strategy reached the freezing point at 17 s when the startup temperature was -10 C, which is faster than other startup strategies. Additionally, the time to ice production was controlled to about 20 s. Compared with the pote... Read More

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This research presents a method for controlling a fuel cell group in an electric vehicle. The method involves dividing a high-power fuel cell stack into multiple small-power fuel cell stacks and starting and stopping them in a grouping manner during the vehicle's operation. The small-power fuel cell stacks are started based on the vehicle's running state and stopped based on the performance degradation of each individual stack. The proposed method improves the efficiency and fuel economy of the power system, reduces performance degradation of fuel cells, extends the service life of the fuel cell power system, and provides significant practical value.

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During the shutdown process of the fuel cell system for vehicles, the air entering the anode chamber can form the hydrogen/air interface, accelerating the carbon corrosion of the catalytic layer. According to optimized control strategies, the carbon corrosion of fuel cells can be reduced. Nowadays, the main control strategies include gas purging and the consumption of residual oxygen in the stack by the auxiliary load. However, the oxygen in the fuel cell stack cannot be fully consumed or can cause the single-cell voltage to rise to 0.8 V with an inappropriate discharge current drop rate and auxiliary load resistance value, thus affecting the protective effect of the shutdown strategy. In this work, a shutdown strategy of the fuel cell system is studied. After the experiment, the optimized value of the discharge current drop rate and the auxiliary load resistance were obtained. With the resistance value of 50 and the current drop rate of 7 A/s, the shutdown time of the fuel cell system is 13.5 s and the time of single-cell voltage above 0.82 V in the fuel cell stack is 0.1 s. Thus,... Read More

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The rapid cold start capability of fuel cell vehicles in low-temperature environments is one of the key factors restricting their commercialization. Reasonable and effective strategies are crucial to improving the low-temperature cold start capability of fuel cell vehicles. In this paper, a cold start model of fuel cell system is established, and the model is verified based on the cold start experiment of a hybrid fuel cell vehicle. The necessity of the coolant preheating strategy in the cold start is analyzed, and the important role of the coolant preheating strategy in helping the fuel cell system to start quickly at -10C and below is demonstrated. Furthermore, the effects of air inlet temperature, air inlet flow rate, and external heater power on the cold start performance are investigated. The results show that when the air inlet temperature rises from -13C to 65C, the start time is shortened from 279 s to 234 s (reduced by 16.13 %). And at low air inlet temperatures, the lower flow rate of air can significantly reduce the temperature difference and maintain uniformity of temp... Read More

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Starting a fuel cell system under subfreezing temperature remains a technological challenge for a large-scale distribution of this kind of power generator, especially in embedded applications. In this paper, investigations on the cold start capabilities of a 700 W proton exchange membrane fuel cell (PEMFC) are performed. The study is based on a potentiostatic control of the load during the start-up procedure. Thanks to the proposed methodology, the fuel cell was able to start without assistance from a temperature of 10 C in 105 s.

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This outstanding PhD thesis describes fuel cells control-oriented models, adaptive online parameter estimation methods and controller design techniques

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The transient and steady-state behaviors of a fuel cell system play an important role to analyze inherent characteristics and design control strategies. In this chapter, a control-oriented model of a fuel cell system is formulated in detail. First, comparison of existing fuel cell models in the literature is discussed and the motivation for establishing a lumped model in this thesis is described in Sect. 2.1. In Sect. 2.2, the general model of fuel cell stack is provided with respect to mass flow balance, electrochemical balance, and thermal energy balance. Moreover, models regarding to solid oxide fuel cell (SOFC) and proton exchange membrane fuel cell (PEMFC) are provided in Sects. 2.3 and 2.4, respectively. Finally, modeling of auxiliary components in the fuel cell system is presented in Sect. 2.5.

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The cold-start of proton exchange membrane fuel cell (PEMFC) has been one of the leading technical challenges for fuel cell vehicle commercialization. During the cold start process, a new control-oriented modelling methodology of a water-cooled PEMFC stack system was present. The voltage and temperature change throughout the stack may be forecast using the model technique. Then the model was validated in a 5 Kw, 20 cells, water-cooled stack at room and subzero temperatures. The result shows that the model accuracy can capture the stationary and transient states of the fuel cell stack well. For the cold start of PEMFCs in automotive applications, the suggested model may be utilized to investigate real-time state estimates and model-based control approaches.

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In the development of fuel cell hybrid vehicles, energy management strategy (EMS) plays an important role. The traditional EMS studies focus on the optimization of energy distribution in order to minimize the hydrogen consumption and degradation cost of fuel cell. However, the phenomenon of fuel cell recoverable performance loss which can affect the efficiency of fuel cell is ignored. Therefore, it is necessary to consider recoverable performance loss in the EMS of fuel cell hybrid power system, which can better simulate practical fuel cell hybrid vehicle scenarios. Although recoverable performance loss can be reversed by performing recovery procedures, fuel cell operation is interrupted during the procedures, thus it is worth studying appropriate time to perform recovery procedures without affecting total power output. To solve these problems, this paper proposed an EMS framework by considering fuel cell recoverable performance. In the study, fuel cell recoverable performance loss is converted to equivalent hydrogen consumption, then an advanced deep reinforcement learning method, D... Read More

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Proton exchange membrane fuel cells (PEMFC) are widely used in various fields due to their low operating temperature, high reliability, fast start-up, and long life. However, fuel cell technology is still severely constrained by its electrical efficiency, price, and lifetime. This paper proposes a power distribution method for multi-stack fuel cell (MFC) system to optimize efficiency and lifetime. A high-efficiency working range is defined to ensure the system efficiency. The startup sequence of each stack is determined by the voltage degradation rate to achieve aging consistency. Three typical methods are compared with the proposed method by simulation, and results show that this distribution method increases the lifespan by 8187% and the efficiency by 33.5%.

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Rapid cold start of proton exchange membrane fuel cell (PEMFC) stack is imperative for the widespread of fuel cell vehicles. In the present work, a two-dimensional transient model of PEMFC stack with coolant recirculation is developed to investigate the cold start characteristics with different strategies. Six different current loading modes are evaluated under 20 C including constant current loading modes and constant slope ramp current loading modes with various current increase rates and different initial water content. The temperature distribution, ice volume fraction distribution in in-plane and through-plane directions, as well as the output voltage, voltage loss, voltage consistency and coolant temperature are monitored and comprehensively analyzed. The results show that a constant slope ramp current loading mode with relatively large initial current density and appropriate initial water content is beneficial to rapid start-up due to the gradual hydration of the membrane and the increase of temperature.

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AbstractsStarting the proton exchange membrane fuel cell (PEMFC) stack at sub-zero temperature is considered as one of the main obstacles to the wide commercial application of fuel cells. In this paper, a cold start model of PEMFC stack is established, and a new start-up method-variable coolant rate and load control (VCRLC) is put forward and evaluated. Its main idea is to control the flow rate of coolant and current density in real time according to the temperature of the PEMFC stack, so as to realize rapid temperature rise and uniform temperature distribution of the stack. Based on this method, the self-heating potential of the stack can be utilized more effectively. In order to better understand the cold start process, the effects of initial water content, convective heat transfer coefficient and coolant flow rate on the ice distribution, temperature distribution and voltage consistency in the PEMFC stack are analyzed and compared in detail. The results show that the VCRLC method can significantly improve the cold start performance of PEMFC stack, which is of great significance to... Read More

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Durability and reliability are the key factors that prevent fuel cells from successful implementation in automotive sector. Dynamic load change is a common and frequent condition that the fuel cell has to undergo in automotive applications. Fuel cells are more sensitive to changes in load conditions and degrade based on load variation representing idling, rated power, and high power operating conditions. To examine the influence of dynamic load step on the fuel cell performance, two similar cells of active 25 cm2 was tested under two different load step for the same dynamic load cycle. The main difference in dynamic load cycle 2 was the ramp rate which was fixed as 0.1, 0.3, and 0.25 A/cm2/s for 0.2, 0.6, and 1.0 A/cm2 respectively. To investigate the degradative effects, polarization curves, electrochemical impedance spectroscopy, and field emission scanning electron microscopy were used. The results indicated that the degradation rate increased in both dynamic load cycles but however the impact of load change was comparatively minimal in dynamic load cycle 2. The total degradation ... Read More

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Using hydrogen fuel cells for power systems, temperature conditions are important for efficient and reliable operations, especially in low-temperature environments. A heating system with an electrical energy buffer is therefore required for reliable operation. There is a research gap in finding an appropriate control strategy regarding energy efficiency and reliable operations for different environmental conditions. This paper investigates heating strategies for the subfreezing start of a fuel cell for portable applications at an early development stage to enable frontloading in product engineering. The strategies were investigated by simulation and experiment. A prototype for such a system was built and tested for subfreezing start-ups and non-subfreezing start-ups. This was done by heating the fuel cell system with different control strategies to test their efficiency. It was found that operating strategies to heat up the fuel cell system can ensure a more reliable and energy-efficient operation. The heating strategy needs to be adjusted according to the ambient conditions, as this... Read More

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This article deals with implementing a rule-based control method and startup sequence of a hybrid electric vehicle powered by a modular fuel cell system as its primary energy source and a lithium-ion battery system as its secondary energy source. The modular fuel cell system is composed of two separate fuel cell systems, electrically coupled to a one-power converter, using a programmable device. Depending on the vehicles operating mode, either both systems are used or just one of them. The vehicles fuel efficiency is improved by operating at constant power in the peak efficiency range of each fuel cell system. The experimental results show that the proposed system can significantly improve the fuel economy of a fuel cell vehicle and extend the driving range, while avoiding start/stop cycles. Additionally, this solution can increase the fuel cells lifecycle.

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Fuel cell performance tests for automotive applications include static and dynamic tests, and the dynamic load test is typically carried out to investigate the cell operating performance related to driving behavior in the particular use of fuel cell electric vehicles. The automatic hydrogen flow controller, utilized to regulate the hydrogen flow as a function of time, is one of the imperative apparatuses applied for the dynamic test. The driving behavior generally consists of rapid load fluctuations, several loads running at idle, full power, overload circumstances, start-stop repeats, and cold starting, and these dynamic variations are directly related to the power required for propelling a vehicle and the demand for hydrogen volume fluctuation throughout time. The desired automatic hydrogen flow controller was designed and manufactured for the dynamic performance test via the driving simulation protocol of a heavy-duty vehicle. The main experimental activities were performed to observe the responsibility and accuracy of the invented controller. The relation between the reliability ... Read More

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PEM fuel cell systems in automotive applications must provide a low minimum power compared to their maximum power. Especially systems without external humidification require a rather low stoichiometry and elevated pressure at the cathode to avoid dry-out at low load operation. Targeted experiments show that this may cause flooding, as the gas velocity becomes too low for sufficient liquid water drainage. An increase of the gas velocity would cause a membrane dry-out, negatively impacting the cells performance and lifetime. One solution for this issue is proposed in this work: a dynamic operation of the air system, which is periodically switched between one set point for membrane humidification and another one for liquid water drainage. A sophisticated experimental fuel cell system is used to test the proposed solution on a 100kW stack.

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In high-powered application scenarios, a multi-stack fuel cell system (MFCS) could have advantages such as higher robustness, lifetime, and reliability than a single-stack fuel cell system. In particular, MFCS could maintain a high efficiency and increase system redundancy by power configuration between subsystems. In order to reduce the operational expenses for systems, a reasonable power management strategy is necessary to minimize the hydrogen consumption of MFCS. First, the power-hydrogen consumption curve of the single-stack fuel cell system is discretized from experimental measurements. Next, the discrete data are reassembled by the inverse derivation of the dynamic programming method to produce a minimum solution for the hydrogen consumption in the output power range. It is found that the strategy varies depending on activated state On or Off. Finally, two power allocation strategies are developed and modeled in a lookup-table block considering the activated state. The optimal stack output power strategy is analyzed with four stacks. The results indicate that the hydrogen cons... Read More

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The environmental adaptability of fuel cell vehicle is a technical problem restricting the commercialization promotion. This paper uses the method of combining theoretical analysis and vehicle test to analyze the thermodynamic performance of the vehicle at different temperatures, and constructs the low-temperature cold start model and heat balance model of the fuel cell system, so as to accurately restore the output power characteristics and temperature characteristics of the fuel cell system in the low-temperature cold start process and high-temperature heat balance process. It provides a reference for the environmental adaptability analysis and optimization of fuel cell vehicles. The vehicle test results show that the established simulation model can better reflect the output state of fuel cell, and the temperature error of fuel cell system is less than 1 C, which provides a reference for the analysis and optimization of fuel cell environmental adaptability in the process of vehicle development, and has strong engineering practical significance.

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Prognosis and Health Management is a powerful approach in the quest to improve fuel cell durability. Prognosis is applied to quantify and predict the fuel cell state of health. By assessing the state of health, fuel cell operating conditions can be adapted to reduce its degradation rate. The objective of this paper is to present a fuel cell prognosis method. An empirical model separating membrane and catalyst degradation is adopted. The model coefficients are estimated using a particle filter. The prediction results are encouraging as the fuel cell voltage can be accurately estimated and predicted. The prognosis method presented in this paper is trained and validated using proton exchange membrane fuel cell stack data, going through a dynamic load profile. This novel experimental data has been generated at Sintef Laboratory, on an automotive fuel cell short stack provided by Symbio.

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Heat and power cogeneration plants based on fuel cells are interesting systems for energy- conversion at low environmental impact. Various fuel cells have been proposed, of which proton-exchange membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC) are the most frequently used. However, experimental testing rigs are expensive, and the development of commercial systems is time consuming if based on fully experimental activities. Furthermore, tight control of the operation of fuel cells is compulsory to avoid damage, and such control must be based on accurate models, able to predict cell behaviour and prevent stresses and shutdown. Additionally, when used for mobile applications, intrinsically dynamic operation is needed. Some selected examples of steady-state, dynamic and fluid-dynamic modelling of different types of fuel cells are here proposed, mainly dealing with PEMFC and SOFC types. The general ideas behind the thermodynamic, kinetic and transport description are discussed, with some examples of models derived for single cells, stacks and integrated power cogeneration uni... Read More

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The transient response of proton exchange membrane fuel cell (PEMFC) during start-up is an important issue for a system.In this paper, the start-up process of the 6-cell stack with the dead-end anode and recirculation cathode is studied.The effects of starting load, step size on voltage variation are studied via the measurement of time evolution of the stack voltage.In addition, the different start-up responses of the singlecell under the flow-through and recirculation are compared.It is found that increasing the start-up current density and reducing the step load change can shorten the start-up time.However, the shorter start-up time will result in the lower critical membrane dehydration temperature.Compared with the gas-through mode, when the stack with dead-end anode and cathode recirculation is started, the single cell near the outlet is more likely to be flooded at the moment of high current density start-up due to the closing of anode outlet.

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Start-Up/Shut-Down phases in PEM Fuel Cell system has paid particular attention because of the well-identified reverse current mechanism leading to harsh corrosion environment within the Cathode Catalyst Layer. In this work, an experimental ageing test is designed to assess a comprehensive investigation of electrochemical properties degradations and thus influence on cell performances during the Start-Up phase. An Accelerated Stress Test protocol is designed to mimic and cycle the cathodic potential profile during the H2|Air front propagation along anodic channel. A sensitivity analysis is performed on the maximum cathodic potential and the exposure time parameters. Results divulge that lowering maximum potential by a dummy load application and lowering exposure time by accelerating H2 feeding during Start-Up phases are promising mitigation strategies. Moreover, this paper reports a promising effect by scanning the cathodic potential above 1.0 V for conditioning carbon support and optimizing cell performance at high current densities.

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Proton exchange membrane fuel cells are promised to be the future choice for transportation power systems.Start-up procedure has significant impacts on fuel cell degradation.Most damages induced by start-up procedure relate to the hydrogen/air interface inside fuel cell.Studying on hydrogen/air interface is crucial for start-up degradation mitigation.It is difficult to monitor the internal distribution and transfer of hydrogen and oxygen by experiments.Therefore, this paper establishes a three-dimensional two-phase fuel cell model to simulate the gas concentration distribution in anode compartment, and proposes a start-up purging strategy by injecting hydrogen into the anode.The hydrogen/air interface removal process is simulated and visualized.Subsequently, the impacts of initial residual oxygen concentration and hydrogen flow rate on air removal in anode compartment are studied.It is proved that decrease initial oxygen concentration and increase hydrogen injection flow rate can significantly shorten the purge time.However, small flow rate of hydrogen injection is more economical fo... Read More

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The cold start of polymer electrolyte fuel cells (PEMFC) remains a challenge for their automotive applications, due to blockage of the electrode pores with frozen or liquid water yielding a lower efficiency or even a failure of the start-up. One solution is the preheating of the PEMFC with a thermochemical preheater, e.g. a metal hydride reactor, which releases heat upon hydrogen absorption. To the authors knowledge, this is the first work presenting a 2D transient physical model for the coupled system of PEMFC and thermochemical preheater. The aims are investigating different cold start strategies and proposing a strategy to achieve rapid start-ups. Internal heating, i.e. only relying on the waste heat of the fuel cell, yields high heating rates, which mainly stems from the Ohmic resistance and the overpotential of the oxygen reduction reaction. According to the simulations, lower cell voltages yield higher heating rates and are thus beneficial for cold starts, e.g. a start-up from -16 C with 0.5 V fails, while the same start with 0.1 V succeeds. However, there is a critical tempe... Read More

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Heat and power cogeneration plants based on fuel cells are interesting systems for energy- conversion at low environmental impact. Different fuel cells have been proposed, but experimental testing rigs are expensive and the development of commercial systems is time consuming if based on fully experimental activities. Furthermore, tight control of operation of fuel cells is compulsory to avoid damage, which must be based on accurate models, able to predict the cell behaviour and prevent stresses and shut-down. Some selected examples of steady state, dynamic and fluid dynamic modelling of different types of fuel cells are proposed, mainly PEMFC and SOFC type. The general ideas behind the thermodynamic, kinetic and transport description are recalled, with some examples of models derived for single cells, stacks and integrated power co-generation units.

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