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.     

Modelling,simulation and control of a proton exchange membrane fuel cell (PEMFC) power system

Fuel cell power systems are emerging as promising means of electrical power generation on account of the associated clean electricity generation process, as well as their suitability for use in a wide range of applications. During the design stage, the development of a computer model for simulating the behaviour of a system under development can facilitate the experimentation and testing of that system's performance. Since the electrical power output of a fuel cell stack is seldom at a suitable fixed voltage, conditioning circuits and their associated controllers must be incorporated in the design of the fuel cell power system. This paper presents a MATLAB/Simulink model that simulates the behaviour of a Proton Exchange Membrane Fuel Cell (PEMFC), conditioning circuits and their controllers. The computer modelling of the PEMFC was based on adopted mathematical models that describe the fuel cell's operational voltage, while accounting for the irreversibilities associated with the fuel cell stack. The conditioning circuits that are included in the Simulink model are a DC–DC converter and DC–AC inverter circuits. These circuits are the commonly utilized power electronics circuits for regulating and conditioning the output voltage from a fuel cell stack. The modelling of the circuits is based on relationships that govern the output voltage behaviour with respect to their input voltages, switching duty cycle and efficiency. In addition, this paper describes a Fuzzy Logic Controller (FLC) design that is aimed at regulating the conditioning circuits to provide and maintain suitable electrical power for a wide range of applications. The model presented demonstrates the use of the FLC in conjunction with the PEMFC Simulink model and that it is the basis for more in-depth analytical models.     

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.     

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.     

A novel PEMFC power conditioning system based on the interleaved high gain boost converter

Power converter units are crucial components in proton exchange membrane fuel cell (PEMFC) energy generation systems. For this reason, and also motivated by the demands in high quality power conditioning for PEMFC systems, we propose the application of an interleaved high gain boost converter topology with a diode clamped multilevel inverter as power interface. The main advantages of the proposed scheme encompass: high voltage conversion ratio, input current ripple mitigation, and voltage balancing across output capacitors. These characteristics make this converter ideal for grid-connection purposes, acting as an interface for renewable energy sources that provide low voltages and demand low current ripples. The underlying theoretical analysis as well as simulation and experimental validation are presented in this paper.     

Improvement of thermal management of proton exchange membrane fuel cell stack used for portable devices by integrating the ultrathin vapor chamber

UVC (ultrathin vapor chamber) simultaneously has a high heat-conducting property, excellent temperature uniformity and simple structure. These advantages are very suitable for thermal management of the open-cathode PEMFC (proton exchange membrane fuel cell) stack. In this work, two-type UVCs with different appearances are integrated into a conventional PEMFC stack respectively. The effect of UVC on the output performance, thermal management and operating stability is investigated by the experiment combined with simulation. The results show that UVC can significantly increase the output voltage under high current density. In 35 A, the output voltage of the stack integrated the vertical UVC increases by 20.25% relative to the conventional stack. Thermal management is also improved by UVC. The highest temperature inside the stack decrease by 9 °C in 35 A, and the membrane temperature is decreased obviously. But it still exceeds the optimal operating temperature of open-cathode PEMFC stack due to the poor cooling type in the condensation side of UVC. UVC improves the operation stability of the stack and slows the deteriorative speed of output performance. This work hopes to attract more attention to the application of UVC on the thermal management of portable power sources used open-cathode PEMFC stack.     

Performance of a PEMFC system integrated with a biogas chemical looping reforming processor: A theoretical analysis and comparison with other fuel processors (steam reforming,partial oxidation and auto-thermal reforming)

In this work, the performance of a PEMFC (proton exchange membrane fuel cell) system integrated with a biogas chemical looping reforming processor is analyzed. The global efficiency is investigated by means of a thermodynamic study and the application of a generalized steady-state electrochemical model. The theoretical analysis is carried out for the commercial fuel cell BCS 500W stack. From literature, chemical looping reforming (CLR) is described as an attractive process only if the system operates at high pressure. However, the present research shows that advantages of the CLR process can be obtained at atmospheric pressure if this technology is integrated with a PEMFC system. The performance of a complete fuel cell system employing a fuel processor based on CLR technology is compared with those achieved when conventional fuel processors (steam reforming (SR), partial oxidation (PO) and auto-thermal reforming (ATR)) are used. In the first part of this paper, the Gibbs energy minimization method is applied to the unit comprising the fuel- and air-reactors in CLR or to the reformer (SR, PO, ATR). The goal is to investigate the characteristics of these different types of reforming process to generate hydrogen from clean model biogas and identify the optimized operating conditions for each process. Then, in the second part of this research, material and energy balances are solved for the complete fuel cell system processing biogas, taking into account the optimized conditions found in the first part. The overall efficiency of the PEMFC stack integrated with the fuel processor is found to be dependent on the required power demand. At low loads, efficiency is around 45%, whereas, at higher power demands, efficiencies around 25% are calculated for all the fuel processors. Simulation results show that, to generate the same molar flow-rate of H₂ to operate the PEMFC stack at a given current, the global process involving SR reactor is by far much more energy demanding than the other technologies. In this case, biogas is burnt in a catalytic combustor to supply the energy required, and there is a concern with respect to CO₂ emissions. The use of fuel processors based on CLR, PO or ATR results in an auto-thermal global process. If CLR based fuel processor is employed, CO₂ can be easily recovered, since air is not mixed with the reformate. In addition, the highest values of voltage and power are achieved when the PEMFC stack is fed on the stream coming from SR and CLR fuel processors. When a H₂ mixture is produced by reforming biogas through PO and ATR technologies, the relative anode overpotential of a single cell is about 55 mV, whereas, with the use of CLR and SR processes, this value is reduced to ∼37 and 24 mV, respectively. In this way, CLR can be seen as an advantageous reforming technology, since it allows that the global process can be operated under auto-thermal conditions and, at the same time, it allows the PEMFC stack to achieve values of voltage and power closer to those obtained when SR fuel processors are used. Thus, efforts on the development of fuel processors based on CLR technology operating at atmospheric pressure can be considered by future researchers. In the case of biogas, the CO₂ captured can produce additional economical benefits in a ‘carbon market’.     

Energy processing from fuel-cell systems using a high-gain power dc-dc converter: Analysis,design, and implementation

The electrolyte membrane fuel cell (PEMFC) is characterized by a low and unregulated output voltage; thus, an interface between source and load is required for processing the generated energy by the PEMFC. In this paper, a solution for processing the energy generated by a PEMFC is given. A switching regulator is developed by using a quadratic boost converter with a single switch (QBC-SS). The controller for the QBC-SS is designed using average current-mode (ACM) control, which is easy to implement using analog circuits. The proposed switching regulator ensures high conversion ratios, output voltage regulation, adequate dynamic performance, and stability. On the other hand, a model with static characteristics for the PEMFC electrical behavior is proposed, which can be used for modeling and control purposes. This model consists of three parameters, which are computed using experimental data of the PEMFC stack. A laboratory prototype of 400 W is used to verify the analytical results. As an input source, a PEMFC system is used. The output voltage of the PEMFC stack ranges from 41 V to 24 V, which depends on the generated current. Experimental results applying load step changes and frequency response analysis are shown.     

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.     

Fractional order modeling and two loop control of PEM fuel cell for voltage regulation considering both source and load perturbations

The growing demand for renewable energy sources has favored attention towards fuel cell and in particular towards Polymer Electrolyte Membrane Fuel Cell (PEMFC) as an alternative energy source. Despite the advantage of possessing high current density, standalone isolated fuel cell operate at low voltage and the output is heavily dependent on the operating condition. This demands the integration of fuel cells with suitable power conditioning units. The present work aims at designing a controller which achieves the objective of regulated output voltage irrespective of variation in both load and source operating condition. The design and integration of the converter with PEMFC necessitates the development of a mathematical model, which can represent the PEMFC dynamics under different operating conditions. PEMFCs are known to exhibit distributed dynamics and possess long term memory, which are more accurately represented by fractional calculus. In this regard, a hybrid optimization based approach for fractional order modeling of PEMFC has been proposed. Further using the model, a fractional order Proportional Integral (FOPI) controller has been designed for regulating the load voltage. The presence of an extra tuning parameter in FOPI allows greater flexibility in achieving the system specification as compared to the classical Integer Order Proportional Integral (IOPI) controller. The effectiveness of the proposed FOPI controller for PEMFC fed PWM DC/DC converter has been validated under varying operating condition of the PEMFC and load perturbations in real time environment.     

Modeling of the Ballard-Mark-V proton exchange membrane fuel cell with power converters for applications in autonomous underwater vehicles

This paper studies the transient response of the output voltages of a Ballard-Mark-V 35-cell 5 kW proton exchange membrane fuel cell (PEMFC) stack with power conversion for applications in autonomous underwater vehicles (AUVs) under load changes. Four types of pulse-width modulated (PWM) dc-dc power converters are employed to connect to the studied fuel cell in series for converting the unregulated fuel cell stack voltage into the desired voltage levels. The fuel cell model in this paper consists of the double-layer charging effect, gases diffusion in the electrodes, and the thermodynamic characteristic; PWM dc-dc converters are assumed to operate in continuous-conduction mode with a voltage-mode control compensator. The models of the study's fuel cell and PWM dc-dc converters have been implemented in a Matlab/SIMULINKTM environment. The results show that the output voltages of the studied PEMFC connected with PWM dc-dc converters during a load change are stable. Moreover, the model can predict the transient response of hydrogen/oxygen out flow rates and cathode and anode channel temperatures/pressures under sudden change in load current.     

A family of high gain fuel cell front-end converters with low input current ripple for PEMFC power conditioning systems

Since the output voltage of the proton exchange membrane fuel cell (PEMFC) is relatively low and load-dependent, a high-performance fuel cell front-end converter is required to achieve boost and power regulation in PEMFC systems. In response, a novel family of high gain fuel cell front-end converters with low input current ripple is proposed. The proposed topologies can substantially improve the voltage gain through the expansion and combination of active switched-inductor networks and passive switched-capacitor units. The introduced interleaved parallel structure is convenient to limit the current ripple on the input side to prevent accelerated aging of fuel cells, which is another prominent advantage. Meanwhile, the converters can achieve the automatic current sharing between parallel inductors and the low voltage stress on active switches and diodes. In this paper, the fuel cell model and topology derivation of the high gain fuel cell front-end converters are first analyzed. Then, it further describes the operating mode and steady-state performance of converters under the inductor current continuous conduction mode. The comparison with other converters shows that this converter is suitable for connecting the PEMFC to the high voltage DC bus. Finally, a 200 W, 20/180 V converter prototype is implemented, and the simulation and experiment prove the theoretical correctness and validate the superior performances of the proposed converters.     

Dynamic modeling and simulation of a small wind–fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind–fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK^TM is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind–fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities.     

PEMFC purging at low operating temperatures: An experimental approach

In this paper, the effect of operating temperature on optimal purge interval for maximum energy efficiency in a proton exchange membrane fuel cell (PEMFC) with dead‐ended anode (DEA) was experimentally investigated. The study was conducted with a focus on challenges associated with operation at temperatures lower than the recommended designed temperature. With DEA, gradual voltage drop happens due to the accumulation of water and impurities such as nitrogen. Hence, periodic purging of the anode side is required to remove excess water and impurities that are accumulated at the anode side over time. Short purge intervals increase hydrogen loss that translates into low fuel utilisation, whereas long purge intervals result in voltage drop due to high water and impurity accumulations. Therefore, an optimal purge strategy should be implemented to maximise the stack energy efficiency. Depending on the operating conditions and loads, there are instances that a fuel cell stack operates at temperatures lower than its recommended designed temperature. Considering the temperature effect on the cell water management, operating temperature is an important factor to consider for optimising the purge strategy in PEMFCs. At lower operating temperatures (ie, below 50°C), more water is formed in liquid form, which makes the optimisation of purge strategy more challenging. For a stack temperature of 40°C, it was observed that with an increase in stack current from 0.25 to 0.45 A cm^?2, the optimal purge interval decreases from 90 seconds to around 45 seconds, respectively. Increasing the stack temperature from 40°C to 50°C resulted in an increase in the optimal purge interval to 120 seconds and 90 seconds for stack currents of 0.25 (ie, low current density) and 0.45 A cm^?2, respectively. At lower operating temperatures, more frequent purging schedules are needed accordingly to remove the liquid water from the cell. These results indicated that at lower operating temperatures, water accumulation at the anode side becomes more dominant compared with higher operating temperatures.     

Connected evaluation of polymer electrolyte membrane fuel cell with dehydrogenation reactor of liquid organic hydrogen carrier

Recently, hydrogen energy technologies attract attention as power systems. To develop hydrogen energy systems, hydrogen storage methods with high storage density and good safety are required. Liquid organic hydrogen carrier (LOHC) is one of the novel hydrogen storage technologies. LOHC has advantages of high storage density, good safety, and easy handling. In this study, a polymer electrolyte membrane fuel cell (PEMFC) stack is operated with hydrogen released from LOHC to evaluate the feasibility of the connected operation of the PEMFC stack and LOHC dehydrogenation reactor. Dibenzyltoluene (H0-DBT) is used as a LOHC material, and the dehydrogenation of perhydro dibenzyltoluene (H18-DBT) is conducted at 240–300 °C. Released hydrogen is purified by adsorbent of activated carbon to remove impurities. However, 100–1400 ppm of methane is observed after the purification, and the PEMFC stack power is reduced from 39.4 W to 39.0 W during the operation by hydrogen dilution and physical adsorption of methane. Then, to evaluate the irreversible damage, pure hydrogen was supplied to the PEMFC stack. The stack power is recovered to 39.4 W. It is concluded that the connected operation of the LOHC dehydrogenation reactor and PEMFC stack is feasible, and the activated carbon adsorbent can be a cost-effective purification method for LOHC.     

Experimental analysis of the performance of the air supply system in a 120 kW polymer electrolyte membrane fuel cell system

For analyzing the performance of 120 kW polymer electrolyte membrane fuel cell (PEMFC) system and its air supply system, an air system test bench was built, then applied on a 120 kW PEMFC system test bench composed of air supply subsystem, hydrogen supply subsystem, stack, cooling subsystem and electronic control subsystem. The strategy composed of feedforward table and Piecewise proportional integral (PI) feedback control strategy is employed to regulate the flow rate and pressure of air supply system. Firstly, the air compressor map and the mapping relationship between the speed of air compressor, opening of back-pressure valve and stack current are obtained by carrying out experiments on the PEMFC air system bench. Then, the max output performance, steady-state performance, the startup performance, the dynamic response abilities of PEMFC system are tested, respectively. During the experiments, performances under different test conditions were analyzed by comparing parameters such as voltage inconsistency, average voltage, minimum voltage, voltage range, net power of the PEMFC system, and stack power. The test results show that the air supply system can provide qualified flow rate and pressure for the PEMFC stack. The peak power of the stack is 120 kW and net power of the system is 97 kW when the current is 538 A. The response time from rated net power to idle net power is 12 s and from idle net power to rated net power is 23 s. The overshoot of average voltage and minimum voltage in the process of increasing load is both 0.01 V, which are 0.015 V and 0.02 V lower than that when the load is decreased, respectively. The dynamic response speed and stability of the PEMFC system in the process of decreasing the load are better than those in the process of increasing the load.     

PEM single fuel cell as a dedicated power source for high-inductive superconducting coils

In practice, the voltage of a hydrogen–oxygen fuel cell is around 1 V at open circuit and from 0.6 V to 0.7 V at full rated load and it can be considered as a low-voltage energy source. Moreover, preliminary investigations undertaken on a single proton exchange membrane fuel cell (PEMFC) highlighted its behavior as a DC current source, that can be directly controlled by the H₂ flow rate when the operating point is at very low voltage. In this paper, we present an innovative application of PEMFC that relies on taking advantage of both low voltage level and current source operating mode to feed a high inductive superconducting coil. Such a coil has no resistance and among others, is very sensitive to current ripples. Thus, specific power supplies are designed to feed them but they exhibit in most cases a huge volume and/or a low energy yield. Connecting a superconducting coil to a PEMFC implies to operate in short-circuit, which is an unusual use of PEMFC. To this end, requirements of such an application are defined, by making use of a PEMFC electrical model based on a 1D analog representation of mass transport phenomena. This model, that enables to take into account the influence of gas supply conditions, notably diffusion limit operation, is directly implemented in a standard simulation software used in electrical engineering. Then, simulation results and experimental results obtained by supplying a 10 H superconducting coil cooled by liquid helium by means of a single 100 cm² PEMFC are compared and discussed.     

Fuel cell power conditioning system design for residential application

This paper presents a design of a high performance proton exchange membrane fuel cell (PEMFC) power conditioning system (PCS) for residential application. Firstly, a high efficiency PCS topology is described which can improve the PCS maximum efficiency up to 92.9%. Furthermore, a novel PCS controller is presented, which succeeds in suppressing the low frequency current ripple, controlling the dc link voltage and inverter output current. The controller also achieves reliable power grid integration. The experimental results show that a residential fuel cell PCS with high performance can be achieved.     

Continuous bubble humidification and control of relative humidity of H2 for a PEMFC system

The proton conductivity of perfluorinated ionomer membrane used in a proton exchange membrane fuel cell (PEMFC) depends largely on the extent of hydration state of the membrane. Sufficient membrane hydration is achieved typically through the humidification of gases prior to feeding them into the fuel cell. Further, hydrogen humidification is known to have a larger impact on the performance of a PEMFC than the oxygen humidification. Bubble humidification has been a widely used method to externally humidify hydrogen. However, to-date a continuous bubble humidification system, which is essential to the continuous operation of the PEMFC system, has not been implemented. The main contributions of this work are (i) a design for continuous humidification of hydrogen for the PEMFC system and (ii) a method to maintain the RH of hydrogen between 93 and 95% (at desired temperature) over a wide range of gas flow rates. One of the key advantages of the proposed design is the flexibility of using recirculated stack coolant water to increase the energy efficiency of the PEMFC system. The design is first tested off-line and then online with a 1 kW stack. Results obtained from both the off-line and online tests indicate that the design successfully meets the demands of an online operation. It is observed that with the use of the proposed humidification scheme, the stack efficiency in terms of power output increases by about 6–19% of the power obtained under dry hydrogen conditions.     

Hydrogen consumption minimization method based on the online identification for multi-stack PEMFCs system

The proton exchange membrane fuel cell (PEMFC) stacks are not widely used in the field of transportation industry, due to their limited power. Thus, the PEMFC stacks usually connected in parallel or series to meet the load demand power in high-power applications. The hydrogen consumption of multi-stack fuel cells (MFCs) system is related to the efficiency and output power. In addition, the efficiency of PEMFC depends on the applied voltage and other parameters. Consequently, the hydrogen consumption of system changes with varying load, because the system parameters are also varying. It makes reducing the fuel consumption of system a challenging assignment. In order to achieve the goal of minimizing fuel consumption of parallel-connected PEMFCs system, this paper proposes a novel power distribution strategy based on forgetting factor recursive least square (FFRLS) online identification. The FFRLS algorithm is based on data-driven and uses real-time data of the system to improve the estimation accuracy of PEMFC system parameters. On the test bench of parallel-connected PEMFCs system consists of two 300 W PEMFC stacks, PEMFC stack controller, DC/DC converters, and DSP controller etc., a multi-index performance test and comparative analysis are carried out. The results showed that, the performance of proposed power allocation strategy has been successfully validated. In addition, compared with the power average and daisy chain algorithms, the proposed online identification power distribution method can get more satisfactory results. Such as, reducing the hydrogen consumption and improving efficiency.