Control-orientated thermal model for proton-exchange membrane fuel cell systems

A lumped parameter dynamic model is developed for predicting the stack temperature, temperatures of the exit reactant gases and coolant water outlet in a proton-exchange membrane fuel cell (PEMFC) system. A dynamic model for a water pump is also developed and can be used along with the thermal model to control the stack temperature. The thermal and water pump models are integrated with the air flow compressor and PEMFC stack current–voltage models developed by Pukrushpan et al. to study the fuel cell system under open and closed-loop conditions. The results obtained for the aforementioned variables from open-loop simulation studies are found to be similar to the experimental values reported in the literature. Closed-loop simulations using the model are carried out to study the effect of stack temperature on settling times of other variables such as stack voltage, air flow rate, oxygen excess ratio and net power of the stack. Further, interaction studies are performed for selecting appropriate input–output pairs for control purpose. Finally, the developed thermal model can assist the designer in choosing the required number of cooling plates to minimize the difference between the cooling water outlet temperature and stack temperature.     

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.     

Identification of the Hammerstein model of a PEMFC stack based on least squares support vector machines

This paper reports a Hammerstein modeling study of a proton exchange membrane fuel cell (PEMFC) stack using least squares support vector machines (LS-SVM). PEMFC is a complex nonlinear, multi-input and multi-output (MIMO) system that is hard to model by traditional methodologies. Due to the generalization performance of LS-SVM being independent of the dimensionality of the input data and the particularly simple structure of the Hammerstein model, a MIMO SVM-ARX (linear autoregression model with exogenous input) Hammerstein model is used to represent the PEMFC stack in this paper. The linear model parameters and the static nonlinearity can be obtained simultaneously by solving a set of linear equations followed by the singular value decomposition (SVD). The simulation tests demonstrate the obtained SVM-ARX Hammerstein model can efficiently approximate the dynamic behavior of a PEMFC stack. Furthermore, based on the proposed SVM-ARX Hammerstein model, valid control strategy studies such as predictive control, robust control can be developed.     

Parameter optimization for a PEMFC model with a hybrid genetic algorithm

Many steady‐state models of polymer electrolyte membrane fuel cells (PEMFC) have been developed and published in recent years. However, models which are easy to be solved and feasible for engineering applications are few. Moreover, rarely the methods for parameter optimization of PEMFC stack models were discussed. In this paper, an electrochemical‐based fuel cell model suitable for engineering optimization is presented. Parameters of this PEMFC model are determined and optimized by means of a niche hybrid genetic algorithm (HGA) by using stack output‐voltage, stack demand current, anode pressure and cathode pressure as input–output data. This genetic algorithm is a modified method for global optimization. It provides a new architecture of hybrid algorithms, which organically merges the niche techniques and Nelder–Mead's simplex method into genetic algorithms (GAs). Calculation results of this PEMFC model with optimized parameters agreed with experimental data well and show that this model can be used for the study on the PEMFC steady‐state performance, is broader in applicability than the earlier steady‐state models. HGA is an effective and reliable technique for optimizing the model parameters of PEMFC stack. Copyright © 2005 John Wiley & Sons, Ltd.     

A study of operation strategy of cooling module with dynamic fuel cell system model for transportation application

A fuel cell system model with detailed cooling module model was developed to evaluate the control algorithms of cooling module which is used for the thermal management of a proton exchange membrane fuel cell (PEMFC) system. The system model is composed of a dynamic fuel cell stack model and a detailed dynamic cooling module model. To extend modeling flexibility, the fuel cell stack model utilizes analytic approach to capture the transient behavior of the stack temperature corresponding to the change of the coolant temperature and the flow rate during load follow-up. The cooling module model integrated model of fan, water pump, coolant passage, and electric motors so that the model is capable of investigation of operating strategy of pump and fan.The fuel cell system model is applied to the investigation of the control logics of the cooling module. Since, it is necessary for the control of cooling module to define the reference conditions such as coolant temperature and fuel cell stack temperature, this study presents such thermal management criteria. Finally, two control algorithms were compared, a conventional control algorithm and a feedback control algorithm. As a consequence, the feedback control algorithm was found to be more suitable for the cooling module of the PEMFC stack, as they consume less parasitic power while producing more stack power compared to a conventionally controlled cooling module.     

Collaborative simulation for dynamical PEMFC power systems

In this paper a collaborative simulation platform for proton exchange membrane fuel cell (PEMFC) power systems is presented, where the stack is simulated by a two-phase distributed parameter model and the auxiliary units by lumped parameter models. By exchanging the dynamic data between the external load/auxiliary units and PEMFC stack, dynamic simulation of PEMFC stack has been carried out during the load changes for various states associated with different characteristic variables. The internal states of the stack can be observed due to variation of external load/auxiliary units. Numerical experiments are provided for a special case with multiple cycles of load changes derived from an acceleration mode of a fuel cell vehicle. The numerical results demonstrate that the “undershoot” of output voltage is due to the response lag of the auxiliary units and liquid water accumulation in the fuel cell stack.     

车用PEMFC氢气系统建模及其排放特性研究

建立基于尾氢再循环的车用PEMFC氢气系统的集总参数模型和质子交换膜燃料电池堆的二维CFD模型,瞬态模拟研究额定功率工况下尾氢排放对系统及电堆工作特性的影响。结果表明：排放过程中,阳极进气压力和进气流量等参数出现显著的波动现象,且波动幅度和波动时间与排放持续时间存在直接关系;电堆性能在排放过程中有所下降,排放结束后能迅速恢复到排放前的水平;阳极内部的水气分布在排放过程中得到明显改善。     

Modeling electrochemical performance in large scale proton exchange membrane fuel cell stacks

The processes, losses, and electrical characteristics of a Membrane-Electrode Assembly (MEA) of a Proton Exchange Membrane Fuel Cell (PEMFC) are described. In addition, a technique for numerically modeling the electrochemical performance of a MEA, developed specifically to be implemented as part of a numerical model of a complete fuel cell stack, is presented. The technique of calculating electrochemical performance was demonstrated by modeling the MEA of a 350 cm², 125 cell PEMFC and combining it with a dynamic fuel cell stack model developed by the authors. Results from the demonstration that pertain to the MEA sub-model are given and described. These include plots of the temperature, pressure, humidity, and oxygen partial pressure distributions for the middle MEA of the modeled stack as well as the corresponding; current produced by that MEA. The demonstration showed that models developed using this technique produce results that are reasonable when compared to established performance expectations and experimental results.     

An integrated simulation model for PEM fuel cell power systems with a buck DC-DC converter

Fuel cell powered systems generally have a high current and a low voltage. Therefore, the output voltage of the fuel cell must be stepped-down using a DC-DC buck converter. However, since the fuel cell and converter have different dynamics, they must be suitably coordinated in order to satisfy the demanded load. Accordingly, this study commences by constructing a MATLAB/Simulink model of a proton exchange membrane fuel cell (PEMFC) system comprising a PEMFC stack, an air/fuel supply system, and a temperature control system. The validity of the PEMFC model is demonstrated by comparing the simulation results obtained for the polarzation curves of a single fuel cell with the corresponding experimental curves. A model is then constructed of the DC-DC buck converter used to step-down the PEMFC output voltage. In addition, a sliding mode control (SMC) scheme is proposed for the DC-DC buck converter which guarantees a low and stable output voltage given transient variations in the output voltage of the PEMFC. Finally, a model is constructed of a DC-AC inverter with a pulse width modulated (PWM) control scheme which enables the PEMFC stack to supply the grid or power AC applications directly. Overall, the combined PEMFC/DC-DC buck converter/DC-AC inverter model provides a powerful and versatile tool for the design and development of a wide range of PEMFC power systems.     

Modeling and thermal management of proton exchange membrane fuel cell for fuel cell/battery hybrid automotive vehicle

The proton exchange membrane fuel cell (PEMFC) stack is a key component in the fuel cell/battery hybrid vehicle. Thermal management and optimized control of the PEMFC under real driving cycle remains a challenging issue. This paper presents a new hybrid vehicle model, including simulations of diver behavior, vehicle dynamic, vehicle control unit, energy control unit, PEMFC stack, cooling system, battery, DC/DC converter, and motor. The stack model had been validated against experimental results. The aim is to model and analyze the characteristics of the 30 kW PEMFC stack regulated by its cooling system under actual driving conditions. Under actual driving cycles (0–65 kW/h), 33%–50% of the total energy becomes stack heat; the heat dissipation requirements of the PEMFC stack are high and increase at high speed and acceleration. A PID control is proposed; the cooling water flow rate is adjusted; the control succeeded in stabilizing the stack temperature at 350 K at actual driving conditions. Constant and relative lower inlet cooling water temperature (340 K) improves the regulation ability of the PID control. The hybrid vehicle model can provide a theoretical basis for the thermal management of the PEMFC stack in complex vehicle driving conditions.     

A high efficient assembly technique for large PEMFC stacks: Part I. Theory

A high efficient assembly technique for large proton exchange membrane fuel cell (PEMFC) stacks is proposed to obtain the optimal clamping load. The stack system is considered as a mechanical equivalent stiffness model consisting of numerous elastic elements (springs) in either series or parallel connections. We first propose an equivalent stiffness model for a single PEM fuel cell, and then develop an equivalent stiffness model for a large PEMFC stack. Based on the equivalent stiffness model, we discuss the effects of the structural parameters and temperature on the internal stress of the components and the contact resistance at the contact interfaces, and show how to determine the assembly parameters of a large fuel cell stack using the equivalent stiffness model. Finally, a three-dimensional finite element analysis (FEA) for a single PEMFC is compared with what the equivalent stiffness model predicts. It is found that the presented model gives very good prediction accuracy for the component stiffness and the clamping load.     

Thermal analysis and management of proton exchange membrane fuel cell stacks for automotive vehicle

The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption.     

A comparative study of single and dual ejector concepts for anodic recirculation system in high-performance vehicular proton exchange membrane fuel cells

The fuel supply system is a critical element in Proton Exchange Membrane Fuel Cell (PEMFC). In vehicular applications, an anode recirculation system (ARS) is required to return residual hydrogen to the fuel line. A 1D model of an ejector-based ARS was created and integrated with a vehicular PEMFC in this study. Therefore, two configurations, single-ejector-based and dual-ejector-based ARS, were developed to regulate the fuel supply and, thus, utilized to examine and conduct a comparative study of their advantages and disadvantages to the dynamic behavior of the stack. The use of ARS was found to improve stack performance and fuel utilization by delivering high stoichiometry, recirculation rate, and relative humidity. Contrary to a single-ejector-based ARS, whose use is restricted due to its limited working range, dual-ejectors can cover all fuel cell stack operating ranges. Sensitivity analysis revealed that primary pressure was the most significant parameter affecting ejector performance and flow characteristics.     

Optimization of fuel cell system operating conditions for fuel cell vehicles

Proton exchange membrane fuel cell (PEMFC) technology for use in fuel cell vehicles and other applications has been intensively developed in recent decades. Besides the fuel cell stack, air and fuel control and thermal and water management are major challenges in the development of the fuel cell for vehicle applications. The air supply system can have a major impact on overall system efficiency. In this paper a fuel cell system model for optimizing system operating conditions was developed which includes the transient dynamics of the air system with varying back pressure. Compared to the conventional fixed back pressure operation, the optimal operation discussed in this paper can achieve higher system efficiency over the full load range. Finally, the model is applied as part of a dynamic forward-looking vehicle model of a load-following direct hydrogen fuel cell vehicle to explore the energy economy optimization potential of fuel cell vehicles.     

Integration of Miniature Heat Pipes into a Proton Exchange Membrane Fuel Cell for Cooling Applications

In proton exchange membrane fuel cell (PEMFC) operations, the electrochemical reactions produce a rise in temperature. A fuel cell stack therefore requires an effective cooling system for optimum performance. In this study, miniature heat pipes were applied for cooling in PEMFC. Three alternatives were considered in tests: free convection, forced convection cooling with air, and also water. An analytical model was developed to show the possibility of evoking heat from inside a fuel cell stack with different numbers of miniature heat pipes. An experiment setup was designed and then used for further analysis. The proposed experiment setup consisted of a simulated fuel cell that produced heat and a number of thermosyphon miniature heat pipes to evoke heat from the simulated fuel cell. The experiment results reported in this paper present advantages and disadvantages of each tested cooling scenario. Results show that each cooling scenario, using a different number of heat pipes, provided different heat removal rates for PEMFC cooling.     

Comprehensive influences measurement and analysis of power converter low frequency current ripple on PEM fuel cell

To deeply understand the influences of power converter's low frequency current ripple (LFCR) and harmonics on a proton exchange membrane fuel cell (PEMFC) in its power conditioning system (PCS), a comprehensive measurement and analysis of the influences of LFCR and harmonics on PEMFC's performance and durability is investigated in this paper. Based on an equivalent circuit model of PEMFC stack and a mechanism model for evaluating the LFCR effects on the PEMFC, this paper studies primarily and systematically the comprehensive influences of LFCR and harmonics on PEMFC performances and durability, such as (1) degrading the PEMFC performance, (2) shortening the lifetime of PEMFC, (3) reducing the stack output power, (4) lowing its availability efficiency, (5) producing more heat and raising the PEMFC temperature, (6) consuming more fuel, and (7) decreasing the fuel utilization. Finally, a Horizon 300 W PEMFC stack is implemented and tested.     

Novel dynamic semiempirical proton exchange membrane fuel cell model incorporating component voltages

This paper introduces a novel dynamic semiempirical model for the proton exchange membrane fuel cell (PEMFC). The proposed model not only considers the stack output voltage but also provides valid waveforms of component voltages, such as the no‐load, activation, ohmic, and concentration voltages of the PEMFC stack system. Experiments under no‐load, ramping load, and dynamic load conditions are performed to obtain various voltage components. According to experimental results, model parameters are optimised using the lightning search algorithm by providing valid theoretical ranges of parameters to the lightning search algorithm code. In addition, the correlation between the vapour and water pressures of the PEMFC is obtained to model the component voltages. Finally, all component voltages and the stack output voltage are validated by using the experimental/theoretical waveforms mentioned in previous research. The proposed model is also compared with a recently developed semiempirical model of PEMFC through particle swarm optimisation. The proposed dynamic model may be used in future in‐depth studies on PEMFC behaviour and in dynamic applications for health monitoring and fault diagnosis.     

Operating characteristics of an air-cooling PEMFC for portable applications

Optimal design and proper operation is important to get designed output power of a polymer electrolyte membrane fuel cell (PEMFC) stack. The air-cooling fuel cell stack is widely used in sub kW PEMFC systems. The purpose of this study is to analyze the operating conditions affecting the performance of an air-cooling PEMFC which is designed for portable applications. It is difficult to maintain well balanced operating conditions. These parameters are the relative humidity, the temperature of the stack, the utility ratio of the reactant gas and so on. In this study a 500 W rate air-cooling PEMFC was fabricated and tested to evaluate the design performance and to determine optimal operating conditions. Moreover, basic modeling also is carried out. These results can be used as design criteria and optimal operating conditions for portable PEMFCs.     

Numerical analysis on the effects of manifold design on flow uniformity in a large proton exchange membrane fuel cell stack

The size and configuration of manifold can affect the flow characteristics and uniformity in proton exchange membrane fuel cell (PEMFC) stack; then its efficiency and service life. Based on the simulation results of a single fuel cell considering electrochemical reaction, a stack model with 300 porous media is established to numerically investigate the performances of a large commercial PEMFC stack. The effects of manifold width and configuration type on the pressure drop and species concentration are studied by computational fluid dynamics (CFD). The results show that the uniformity for most cases of U-type configuration is better than those of Z-type configuration. For U-type configuration, a very good uniformity can be obtained by selecting anode inlet manifold width of 20 mm and anode outlet manifold in range from 25 to 30 mm; the uniformity is bad for all cathode inlet manifold width, relatively better uniformity can be achieved by adjusting cathode outlet manifold width. For Z-type configuration, bad uniformity is found for cathode inlet and outlet manifold with all width; a relatively good uniformity can be obtained with suitable anode manifold width of 35 mm. The research can provide some references to improve gas distribution uniformity in large PEMFC stacks.