Faults diagnosis for PEM fuel cell system based on multi-sensor signals and principle component analysis method

Fuel cell vehicles are becoming more popular and attracting more attention from industries, but stability and reliability of the fuel cell system (FCS) are still problems for its commercial progress. Therefore, a fault diagnosis system is essential for a reliable and long working lifetime FCS. In this work, a fault diagnosis method based on multi-sensor signals and principle component analysis (PCA) is proposed to improve FCS performance. By using this method, the correlation among different sensor signals are analyzed based on multi-sensor signals, and a simplified statistic index for fault diagnosis is deduced based on the PCA. The FCS operation conditions are monitored online, and faults in sensor and system levels are diagnosed. Experimental results show that, two typical fault scenarios, i.e., a single sensor fault and a serious system failure, can be successfully diagnosed and distinguished. For the single sensor fault, the sensor signal is reconstructed immediately to ensure that fuel cell vehicles operate normally. For the system failure, the fault can be detected in 17 s and the fault source signals can be located in 31 s, so the fuel cell stack can be protected timely. The main contribution of this work is to deduce a simplified statistic index for fault diagnosis based on multi-sensor signals and PCA method, and to provide an experimental study on identifying faults in sensor and system levels of a PEM fuel cell system.     

A transient semi-empirical voltage model of a fuel cell stack

On the basis of a case study, we first analyze the voltage transient properties of a fuel cell stack. We then propose a semi-empirical model, which has been validated by three test runs in the paper. The results obtained in this paper show that the model-computed values correctly fit the experimental data and ensure that the suggested model is highly able to reflect the transient properties of the fuel cell stack voltage. The advantage of this model lies in a simple structure, represented by a small number of parameters. Therefore, it can easily be applied to the simulation of vehicle dynamics for design aims.     

Cell voltage monitoring All-in-One. A new low cost solution to perform degradation analysis on air-cooled polymer electrolyte fuel cells

In this work, a new low-cost and high-performance system for cells voltage monitoring and degradation studies in air-cooled polymer electrolyte fuel cells has been designed, built and validated in the laboratory under experimental conditions.This system allows monitoring in real time the cells’ voltages, the stack current and temperature in fuel cells made of up to 100 cells. The developed system consists of an acquisition system, which complies with all the recommendations and features necessary to perform degradation tests. It is a scalable configuration with a low number of components and great simplicity. Additionally, the cell voltage monitoring (CVM) system offers high rate of accuracy and high reliability and low cost in comparison with other commercial systems.In the same way, looking for an "All-in-One" solution, the acquisition hardware is accompanied by a software tool based on the "plug and play" philosophy. It allows in a simple way obtaining information from the cells and performing a degradation analysis based on the study of the polarisation curve. The different options and tools included in the CVM system permit, in a very intuitive and graphical way, detecting and quantifying the cell degradation without the need of isolating the stack from the system.Experimental tests carried out on the system validate its performance and show the great applicability of the system in cases where cell faults detection and degradation analysis are required.     

Operating line analysis of fuel processors for PEM fuel cell systems

At least three different definitions of fuel processor efficiency are in widespread use in the fuel cell industry. In some instances the different definitions are qualitatively the same and differ only in their quantitative values. However, in certain limiting cases, the different efficiency definitions exhibit qualitatively different trends as system parameters are varied. In one limiting case that will be presented, the use of the wrong efficiency definition can lead a process engineer to believe that a theoretical maximum in fuel processor efficiency exists at a particular operating condition, when in fact no such efficiency optimum exists. For these reasons, the objectives of this paper are to: (1) quantitatively compare and contrast these different definitions, (2) highlight the advantages and disadvantages of each definition and (3) recommend the correct definition of fuel processor efficiency.     

A robust online energy management strategy for fuel cell/battery hybrid electric vehicles

Traditional optimization-based energy management strategies (EMSs) do not consider the uncertainty of driving cycle induced by the change of traffic conditions, this paper proposes a robust online EMS (ROEMS) for fuel cell hybrid electric vehicles (FCHEV) to handle the uncertain driving cycles. The energy consumption model of the FCHEV is built by considering the power loss of fuel cell, battery, electric motor, and brake. An offline linear programming-based method is proposed to produce the benchmark solution. The ROEMS instantaneously minimizes the equivalent power of fuel cell and battery, where an equivalent efficiency of battery is defined as the efficiency of hydrogen energy transforming to battery energy. To control the state of charge of battery, two control coefficients are introduced to adjust the power of battery in objective function. Another penalty coefficient is used to amend the power of fuel cell, which reduces the load change of fuel cell so as to slow the degradation of fuel cell. The simulation results indicate that ROEMS has good performance in both fuel economy and load change control of fuel cell. The most important advantage of ROEMS is its robustness and adaptivity, because it almost produces the optimal solution without changing the control parameters when driving cycles are changed.     

Evaluation of an on-site cell voltage monitor for fuel cell systems

Laboratory high performance test equipment is too expensive and bulky for on-site fuel cell stack evaluation. Yet cell voltage monitoring appears from safety assessments to be a crucial element in operating a fuel cell system. In this paper a dedicated cell voltage monitoring system for on-site applications is evaluated. It describes the specific concept of the on-site monitor system, shows measurement results of its specifications for safety, control and long-term evaluation and presents a comprehensive comparison with laboratory equipment.     

PEM fuel cell modeling using system identification methods for urban transportation applications

This paper presents a comparative study of Proton Exchange Membrane (PEM) Fuel Cell (FC) models for integration in hybrid propulsion systems, based on a commercial FC from Nuvera, which is especially manufactured for this application. An existing model is used as a reference in order to build dynamical mathematical models which describe its dynamical behavior in the time domain. These mathematical models are obtained by applying system identification techniques to the reference model. The proposed FC models have been tested through simulations for the real drive cycle of the existing Metro Centro tramway in Seville.     

Power management strategy for vehicular-applied hybrid fuel cell/battery power system

In this paper, a control strategy for a hybrid PEM (proton exchange membrane) fuel cell/BES (battery energy system) vehicular power system is presented. The strategy, based on fuzzy logic control, incorporates the slow dynamics of fuel cells and the state of charge (SOC) of the BES. Fuel cell output power was determined according to the driving load requirement and the SOC, using fuzzy dynamic decision-making and fuzzy self-organizing concepts. An analysis of the simulation results was conducted using Matlab/Simulink/Stateflow software in order to verify the effectiveness of the proposed control strategy. It was confirmed that the control scheme can be used to improve the operational efficiency of the hybrid power system.     

Analytical fuel cell modeling; non-isothermal fuel cells

The isothermal fuel cell model, given in an earlier publication, will be generalized to describe the behaviour of non-isothermal fuel cells of co-flow type. To this end the temperalure distribution inside a fuel cell in steady state is investigated analytically. A simplified relation between the local temperature and the fuel utilization is derived and its practical significance elucidated. Furthermore, it is shown that the solution of the non-isothermal model is accurately approximated by analytical expressions obtained from a so-called quasi-isothermal approach. This new approach yields a similar expression for the cell voltage as derived from the isothermal model. The quasi-isothermal approach is also used to make a clear comparison between the isothermal and the non-isothermal fuel cell model.     

Hydrogen refueling stations and fuel cell buses four year operational analysis under real-world conditions

Worldwide about 550 hydrogen refueling stations (HRS) were in operation in 2021, of which 38% were in Europe. With their number expected to grow even further, the collection and investigation of real-world station operative data are fundamental to tracking their activity in terms of safety issues, performances, maintenance, reliability, and energy use. This paper analyses the parameters that characterize the refueling of 350 bar fuel cell buses (FCB) in five HRS within the 3Emotion project. The HRS are characterized by different refueling capacities, hydrogen supply schemes, storage volumes and pressures, and operational strategies. The FCB operate over various duty cycles circulating on urban and extra-urban routes. From data logs provided by the operators, a dataset of four years of operation has been created. The results show a similar hydrogen amount per fill distribution but quite different refueling times among the stations. The average daily mass per bus and refueling time are around 14.62 kg and 10.28 min. About 50% of the total amount of hydrogen is dispensed overnight, and the refueling events per bus are typically every 24 h. On average, the buses' time spent in service is 10 h per day. The hydrogen consumption is approximately 7 kg/100 km, a rather effective result reached by the technology. The station utilization is below 30% for all sites, the buses availability hardly exceeds 80%.     

Optimization of hydrogen feeding procedure in PEM fuel cell systems for transportation

The hydrogen feeding sub-system is one of balance of plant (BOP) components necessary for the correct operation of a fuel cell system (FCS). In this paper the performance of a 6 kW PEM (Proton Exchange Membrane) FCS, able to work with two fuel feeding procedures (dead-end or flow-through), was experimentally evaluated with the aim to highlight the effect of the anode operation mode on stack efficiency and durability. The FCS operated at low reactant pressure (<50 kPa) and temperature (<330 K), without external humidification. The experiments were performed in both steady state and dynamic conditions. The performance of some cells in dead-end mode worsened during transient phases, while a more stable working was observed with fuel recirculation. This behavior evidenced the positive role of the flow-through procedure in controlling flooding phenomena, with the additional advantage to simplify the management issues related to hydrogen purge and air stoichiometric ratio. The flow-through modality resulted a useful way to optimize the stack efficiency and to reduce the risks of fast degradation due to reactant starvation during transient operative phases.     

A miniature direct formic acid fuel cell battery

This work describes miniature formic acid fuel cell batteries, which are built based on a Nafion^® membrane and thin metal foils. The intrinsic advantages of formic acid fuel allow for a very simple design of the fuel cell, and the volume of the complete system, including fuel reservoir, can be as small as 11 mm³. This work examines the effect of membrane thicknesses and fuel concentrations on the cell performance. The optimized cell performance is obtained with N117 membrane and 12 M fuel. Peak power density of the optimized cell is 112 mW cm⁻². Life tests are conducted at various conditions using 6 μL of fuel. An energy density of 70 Wh L⁻¹ with 40% fuel utilization rate is observed when 12 M formic acid is used at 0.5 V.     

Premixed hydrogen-air combustion system for fuel cell systems

The advance of efficient hydrogen-air combustion systems has increasingly become of interest in the framework of the development of fuel cell systems, especially for the automotive sector. Therefore, compact modulating systems are required, with the additional demand of low emissions, to be integrated in a fuel cell system. A modulating combustion system based on combustion within inert porous media and an integrated heat exchanger has been developed and investigated. The system is able to handle premixed combustion of lean H₂/air mixtures at a surface load range of 1075 kW/m²-2150 kW/m², and a global equivalence ratio of ?=0.5. The special hydrogen-air mixing concept eliminates the risk of flame flashback and enables operation with very low NO_x emissions.     

Sizing of a fuel cell electric vehicle: A pinch analysis-based approach

Polymer electrolyte fuel cells are considered as a promising alternative to mitigate the CO₂ emission in the transport sector. To achieve an efficient and cost-effective system, hybridisation of the energy storage system with a fuel cell is important. Efficient management of energy is the key in order to achieve an efficient and cost-effective configuration for fuel cell electric vehicle. Optimum sizing of the power source and energy storage system, which is capable of meeting the load requirement of the driving cycle is the key challenge for achieving efficient and cost-effective system. In this work, an alternative methodology based on the principles of pinch analysis is proposed, for sizing the energy storage system and the fuel cell for fuel cell-based electric vehicle, and validated for the Worldwide Harmonized Light Vehicle Test Cycle (WLTC) class-3 driving cycle.     

Fault diagnosis of SOFC system based on single cell voltage analysis

The commercialization of Solid Oxide Fuel Cell (SOFC) systems is restricted by the low reliability and durability severely. Generally, a SOFC system includes stack, combustion chamber, fuel heat exchanger, air heat exchanger, steam generator, reformer, and blower, etc. Faults of any part of the SOFC system will affect the performance of the entire system at any time, causing a decrease in the durability and reliability. Therefore, more and more attention has focused on the fault diagnosis technology on the SOFC system lifetime research. However, the practicability of current fault diagnosis algorithm is not enough on account of the redundant fault signals. This paper proposed an improved algorithm for the fault diagnosis using the single cell voltage as the only fault characteristic signal. The voltage signal in time domain with four representative system faults (stack degradation failure, reformer degradation failure, fuel leakage failure, and air leakage failure) are generated by simulation. The fault voltage signal in frequency domain is obtained by Fourier transform of voltage signal in time domain. Then the characteristics of the fault voltage signal in time domain and in frequency domain are extracted, and the voltage performance of fault signal in time domain are analyzed. The single fault and simultaneous fault were diagnosed for four representative system faults and their combination using a suitable classifier. Both types of the fault diagnoses have achieved good recognition effects, which fully verified the feasibility of this improved algorithm.     

Optimization of powerplant component size on board a fuel cell/battery hybrid bus for fuel economy and system durability

The size of the individual powerplant components on board a fuel cell/battery hybrid vehicle affects the power management strategy which determines both the fuel economy and the durability of the fuel cell and the battery, and thus the average lifetime cost of the vehicle. Cost is one of the major barriers to the commercialization of fuel cell vehicles, therefore it is important to study how the sizing configuration affects overall vehicle cost. In this paper, degradation models for the fuel cell and the battery on board a fuel cell/battery hybrid bus are incorporated into the power management system to extend their lifetimes. Different sizing configurations were studied and the results reveal that the optimal size with highest lifetime and lowest average cost is highly dependent on the drive cycle. The vehicle equipped with a small fuel cell stack serving as a range extender will fail earlier and consume more fuel under drive cycles with high average power demand resulting in higher overall cost. However, the same configuration gives optimal results under a standard bus cycle with lower average power demand. At the other end of the spectrum, a fuel cell-dominant bus does not guarantee longer lifetime since the fuel cell operates mostly under low-load conditions which correspond to higher potentials reducing lifetime. Such a configuration also incurs a higher initial capital cost of the fuel cell stack resulting in a high average cost. The best configuration is a battery-dominated system with moderately-sized fuel cell stack which achieves the longest lifetime combined with the lowest average running cost throughout the lifetime of the vehicle.     

Comparative analysis of battery electric,hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system

This paper compares battery electric vehicles (BEV) to hydrogen fuel cell electric vehicles (FCEV) and hydrogen fuel cell plug-in hybrid vehicles (FCHEV). Qualitative comparisons of technologies and infrastructural requirements, and quantitative comparisons of the lifecycle cost of the powertrain over 100,000 mile are undertaken, accounting for capital and fuel costs. A common vehicle platform is assumed. The 2030 scenario is discussed and compared to a conventional gasoline-fuelled internal combustion engine (ICE) powertrain. A comprehensive sensitivity analysis shows that in 2030 FCEVs could achieve lifecycle cost parity with conventional gasoline vehicles. However, both the BEV and FCHEV have significantly lower lifecycle costs. In the 2030 scenario, powertrain lifecycle costs of FCEVs range from $7360 to $22,580, whereas those for BEVs range from $6460 to $11,420 and FCHEVs, from $4310 to $12,540. All vehicle platforms exhibit significant cost sensitivity to powertrain capital cost. The BEV and FCHEV are relatively insensitive to electricity costs but the FCHEV and FCV are sensitive to hydrogen cost. The BEV and FCHEV are reasonably similar in lifecycle cost and one may offer an advantage over the other depending on driving patterns. A key conclusion is that the best path for future development of FCEVs is the FCHEV.     

Performance analysis of proton-exchange membrane fuel cell stacks used in Beijing urban-route buses trial project

Fuel cell hybrid vehicles' sustained development and commercialization are contingent on the reliability and durability of the fuel cell engines. In August 2008, official trial of the three proton-exchange membrane (PEM) fuel cell hybrid city buses commenced in a commercial-operation urban-route in Beijing for one year. In this paper, data from the performance analysis of the automotive fuel cells used in those city buses are presented and analyzed. The durability and reliability of the fuel cell engines under realistic conditions were evaluated by analyzing the standard deviation of the single-cell fuel cell voltages and by estimating the voltage vs. current characteristics obtained using the recursive least squares fitting method. After studying the degradation status by analyzing fitted results from the measured data, it is concluded that the fuel cell engines' performance meets the standard imposed by the driving conditions of the Beijing urban-routes, but that their performance degradation necessitates maintenance in order to ensure normal operation.     

Analysis of proton exchange membrane fuel cells voltage drops for different operating parameters

Fuel cells are devices that convert hydrogen into electric power using electrochemical reactions. It is an essential to understand the underlying dynamic behaviour of proton exchange membrane (PEM) fuel cells and optimize their performance. In this paper, the analysis of activation, ohmic and mass transport voltage drop is viewed. Different operating parameters such as the exchange current density, the transfer coefficient, electrolyte thickness, cell useful area and temperature effect on the voltage-current density curve are simulated. The results show that the voltage drops decrease the voltage and efficiency of the cell. Activation voltage drop reduces the voltage of about 0.2 V, ohmic voltage drop up to 0.8 V and mass transport to nearly to 1 V in high current densities. In addition, high pressures of hydrogen, oxygen and water lead to an increasing of the cell output power. Moreover, the temperature affects the performance of the cell that is reduced in low operating temperature conditions.