The analysis for the efficiency properties of the fuel cell engine

In this paper, the efficiency properties of the single fuel cell and the fuel cell stack have been analyzed theoretically, and the efficiency models of the fuel cell stack and fuel cell engine (FCE) are developed. Through experimental studies, we analyze the relationships between (1) the efficiency of the fuel cell stack and its current, (2) the efficiency of the fuel cell stack and its power, (3) the efficiency of the fuel cell stack and the hydrogen consumption ratio, (4) the efficiency of the FCE and the fuel cell stack current, (5) the efficiency of the FCE and its power, and (6) the efficiency of the FCE and the hydrogen consumption ratio. The factors which affect the efficiency of the fuel cell stack and that of the FCE are discussed. Finally, the efficiency models of the fuel cell stack and the FCE discussed in this paper are verified by test data. The results show that the simulation values fit well with the test data, and they can be applied in the fuel cell vehicle simulation studies.     

Disturbance decoupling control of an ultra-high speed centrifugal compressor for the air management of fuel cell systems

This paper presents a control solution based on dynamic disturbance decoupling control (DDC) for a centrifugal compression system, which is used to supply the compressed air to the fuel cell, thereby reacting with the hydrogen to produce electricity. As a result of its ultra-high speed, this compressor has a great advantage of ultra-compactness, which makes it more suitable for transportation applications. However, unlike positive displacement compressors, the centrifugal compressor has strong coupling between mass flow and pressure, which gives rise to the difficulty of control and also limits its operating region. In this paper, a unique dynamic DDC strategy, based on the active disturbance rejection control (ADRC) framework, is developed to control the mass flow and pressure simultaneously. The experimental results show that, compared with a traditional PI controller this controller performs better in both the transient and steady states. This control system has been validated on a 10 kW fuel cell model under load variations.     

Model-based power control strategy development of a fuel cell hybrid vehicle

An integrated procedure for math modeling and power control strategy design for a fuel cell hybrid vehicle (FCHV) is presented in this paper. Dynamic math model of the powertrain is constructed firstly, which includes four modules: fuel cell engine, DC/DC inverter, motor-driver, and power battery. Based on the mathematic model, a power control principle is designed, which uses full-states closed-loop feedback algorithm. To implement full-states feedback, a Luenberger state observer is designed to estimate open circuit voltage (OCV) of the battery, which make the control principle not sensitive to the battery SOC (state of charge) estimated error. Full-states feedback controller is then designed through analyzing step responding of the powertrain and test data. At last of the paper, the results of simulation and field test are illustrated. The results show that the power control strategy designed takes into account the performance and economy characteristics of components of the FCHV powertrain and achieves the control object excellently.     

Economic energy management strategy design and simulation for a dual-stack fuel cell electric vehicle

This paper presents the design and simulation validation of two energy management strategies for dual-stack fuel cell electric vehicles. With growing concerns about environmental issues and the fossil energy crisis, finding alternative methods for vehicle propulsion is necessary. Proton exchange membrane (PEM) fuel cell systems are now considered to be one of the most promising alternative energy sources. In this work, the challenge of further improving the fuel economy and extending the driving range of a fuel cell vehicle is addressed by a dual-stack fuel cell system with specific energy management strategies. An efficiency optimization strategy and an instantaneous optimization strategy are proposed. Simulation validation for each strategy is conducted based on a dual-stack fuel cell electric vehicle model which follows the new European driving cycle (NEDC). Simulation results show that a dual-stack fuel cell system with proposed energy management strategies can significantly improve the fuel economy of a fuel cell vehicle and thus lengthen the driving range while being able to keep the start-stop frequency of the fuel cell stack within a reasonable range.     

Optimal vehicle control strategy of a fuel cell/battery hybrid city bus

In this article, an optimal vehicle control strategy based on a time-triggered controller area network (TTCAN) system for a polymer electrolyte membrane (PEM) fuel cell/nickel-metal hydride (Ni-MH) battery powered city bus is presented. Aiming at improving the fuel economy of the city bus, the control strategy comprises an equivalent consumption minimization strategy (ECMS) and a braking energy regeneration strategy (BERS). On the basis of the introduction of a battery equivalent hydrogen consumption model incorporating a charge-sustaining coefficient, an analytical solution to the equivalent consumption minimization problem is given. The proposed strategy has been applied in several city buses for the Beijing Olympic Games of 2008. Results of the “China city bus typical cycle” testing show that, the ECMS and the BERS lowered hydrogen consumption by 2.5% and 15.3% respectively, compared with a rule-based strategy. The BERS contributes much more than the ECMS to the fuel economy, because the fuel cell system does not leave much room for the optimal algorithm in improving the efficiency.     

Optimization based energy management strategy for fuel cell/battery/ultracapacitor hybrid vehicle considering fuel economy and fuel cell lifespan

Optimization of energy management strategy (EMS) for fuel cell/battery/ultracapacitor hybrid electrical vehicle (FCHEV) is primarily aimed on reducing fuel consumption. However, serious power fluctuation has effect on the durability of fuel cell, which still remains one challenging barrier for FCHEVs. In this paper, we propose an optimized frequency decoupling EMS using fuzzy control method to extend fuel cell lifespan and improve fuel economy for FCHEV. In the proposed EMS, fuel cell, battery and ultracapacitor are employed to supply low, middle and high-frequency components of required power, respectively. For accurately adjusting membership functions of proposed fuzzy controllers, genetic algorithm (GA) is adopted to optimize them considering multiple constraints on fuel cell power fluctuation and hydrogen consumption. The proposed EMS is verified by Advisor-Simulink and experiment bench. Simulation and experimental results confirm that the proposed EMS can effectively reduce hydrogen consumption in three typical drive cycles, limit fuel cell power fluctuation within 300 W/s and thus extend fuel cell lifespan.     

Diagnostic of fuel cell air supply subsystems based on pressure signal records and statistical pattern recognition approach

A data-driven and application-oriented diagnosis tool is developed for Fuel Cell (FC) air supply subsystems. A bench emulating a FC air line is built to study normal and abnormal operations (clogged inlet, air leakage, error in compressor speed control) and data are collected using the air pressure transducer, which is usually implemented in FC generators. A pattern recognition approach is then applied to statistical features extracted from the pressure signal. The performance of the diagnosis strategy is evaluated from confusion matrices, associated to graphs and performance indicators. Two examples of compressors, air subsystem managements, and data records are considered to examine the method portability. Best classification rates (>95%) are obtained on test profiles, when the pressure regulation is disabled; fault stamps can thus be found in the pressure signal morphology. Regarding the frequency of data logging, both 1 kHz and 100 Hz values are found effective for fault isolations.     

Energy management strategy based on fuzzy logic for a fuel cell hybrid bus

Fuel cell vehicles, as a substitute for internal-combustion-engine vehicles, have become a research hotspot for most automobile manufacturers all over the world. Fuel cell systems have disadvantages, such as high cost, slow response and no regenerative energy recovery during braking; hybridization can be a solution to these drawbacks. This paper presents a fuel cell hybrid bus which is equipped with a fuel cell system and two energy storage devices, i.e., a battery and an ultracapacitor. An energy management strategy based on fuzzy logic, which is employed to control the power flow of the vehicular power train, is described. This strategy is capable of determining the desired output power of the fuel cell system, battery and ultracapacitor according to the propulsion power and recuperated braking power. Some tests to verify the strategy were developed, and the results of the tests show the effectiveness of the proposed energy management strategy and the good performance of the fuel cell hybrid bus.     

Simulation research on a novel control strategy for fuel cell extended-range vehicles

Adapting to urban transportation and emission reduction in China, fuel cell extended-range commercial vehicles are advocated and studied, which have the advantages of no pollution and long continued driving mileage. According to the features of fuel cell extender and characteristics of the powertrain system of the electric commercial vehicle, the design principle of the extender control strategy is determined in this paper, in order to improve the power and economic performance. A simulation platform for fuel cell plus electric vehicles was established. By comparing and analyzing the characteristics of on-off control strategy, power following control strategy and fuzzy logic control strategy, an on-off power following control strategy is put forward and built which is used for extender controller, and a fuzzy algorithm of following control strategy is studied. By Simulating and analyzing on the platform, the results show that the power following fuzzy algorithm can improve the power performance with the 8.9s accelerating time (0–50 km/h) and better total mileage continued 286.7 km for the powertrain system of fuel cell extended-range commercial vehicles. The research in this paper provides a basis for the in-depth study of the energy management of electric vehicles.     

Development of planar air breathing direct methanol fuel cell stacks

In this paper, design criteria and development techniques for planar air breathing direct methanol fuel cell stacks are described in detail. The fuel cell design in this study incorporates a window-frame structure that provides a large open area for more efficient mass transfer and is modular, making it possible to fabricate components separately. The membrane electrode assembly and gas diffusion layers are laminated together to reduce contact resistance, which eliminates the need for heavy hardware. The composite current collector is low cost, has high electrical conductivity and corrosion resistance. In the interest of quick and cost-efficient prototyping, the fabrication techniques were first developed on a single cell with an active area of 1.0 cm². Larger single cells with active areas of 4.5 and 9.0 cm² were fabricated using techniques based on those developed for the smaller single cell. Two four-cell stacks, one with a total active area of 18.0 cm² and the other with 36.0 cm², were fabricated by inter-connecting four identical cells in series. These four-cell stacks are suitable for portable passive power source applications. The performance analysis of single cells as well as stacks is presented. Peak power outputs of 519.0 and 870.0 mW were achieved in the stacks with active areas of 18.0 and 36.0 cm², respectively. The effects of methanol concentration and fuel cell self-heating on the fuel cell performance are emphasized.     

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.     

An Analytic Hierarchy Process to evaluate PEM fuel cell engine performance

An evaluation model of PEM fuel cell engine (FCE) performance is developed, which provides a new method for a quantitative assessment of FCE performance. Some basic properties and their sub-performance indexes are proposed to evaluate overall performance by analyzing FCE properties, and then the Analytic Hierarchy Process (AHP) theory is used to obtain weighted values of the indexes. Proper scoring functions are established to convert the index values into scores and finally we get an overall score of FCE performance. An example for a real FCE evaluation is also given to illustrate the method.     

Environmental sensor system for expanded capability of PEM fuel cell use in high air contaminant conditions

A novel device called the Environmental Sensor System has been designed and demonstrated to provide real time environmental air contaminant analysis and monitoring to allow fuel cell control systems to protect the integrity of the fuel cell from environmental contaminants. This is accomplished through continuous sampling of the ambient air used to provide oxygen to the fuel cell. Electrochemical sensors are used in this prototype device to monitor hydrogen sulfide, sulfur dioxide, nitric oxide, nitrogen dioxide and volatile organic compounds. The air is monitored before and after the air filter to allow for preventative maintenance and emergency protection. The integration of this ancillary device will allow fuel cell systems to safely and reliably operate in high air contaminant conditions which previously would have resulted in stack poisoning from air contaminants. Preliminary demonstration of this technology to protect the stack on a fuel cell electric bus is reported.     

Research on ADHDP energy management strategy for fuel cell hybrid power system

Fuel cell hybrid power system is a prospective power source for electrical vehicles. To reduce hydrogen consumption and enhance dynamic performance of the system, Action Dependent Heuristic Dynamic Programming (ADHDP) energy management strategy for the fuel cell hybrid power system was proposed. Firstly, topology of the system was analyzed and mathematical model was established through mechanism analysis. Secondly, framework of the ADHDP algorithm was presented, and it was followed by training algorithm for evaluating network and executing network of ADHDP based on Back Propagation (BP) algorithm. Finally, hardware-in-the-loop (HIL) simulation of the fuel cell hybrid power system was carried out to demonstrate the proposed ADHDP algorithm under real operating conditions. The results show that evaluating network and executing network of ADHDP have good convergence performance under different operating conditions. Compared with the other algorithms, the proposed ADHDP energy management strategy has better fuel economy and dynamic performance.     

Energy management of a fuel cell hybrid ultra-energy efficient vehicle

This paper focuses on energy management in an ultra-energy efficient vehicle powered by a hydrogen fuel cell with rated power of 1 kW. The vehicle is especially developed for the student competition Shell Eco-marathon in the Urban Concept category. In order to minimize the driving energy consumption a simulation model of the vehicle and the electric propulsion is developed. The model is based on vehicle dynamics and real motor efficiency as constant DC/DC, motor controllers and transmission efficiency were considered. Based on that model five propulsion schemes and driving strategies were evaluated. The fuel cell output parameters were experimentally determined. Then, the driving energy demand and hydrogen consumption was estimated for each of the propulsion schemes. Finally, an experimental study on fuel cell output power and hydrogen consumption was conducted for two propulsion schemes in case of hybrid and non-hybrid power source. In the hybrid propulsion scheme, supercapacitors were used as energy storage as they were charged from the fuel cell with constant current of 10 A.     

A comprehensive review of energy management optimization strategies for fuel cell passenger vehicle

With the gradual maturity of fuel cell vehicle technology, it gives a better opportunity for the application of passenger vehicles. In this paper, the energy management optimization strategies of fuel cell passenger vehicle (FCPV) are summarized for the first time. Initially, in this review, the topological configurations of FCPV are classified systematically. The optimization objectives, energy consumption and fuel cell life, are proposed for FCPV. Then the energy management strategies (EMSs) are illustrated and analysed based on the optimization objectives above. In terms of the complex and changeable characteristics of FCPV driving conditions, the latest FCPV EMSs which depend on driving information prediction technologies are discussed and summarized. The purpose of this paper is providing references for the development of new generation FCPV energy management optimization strategies.     

Air mass flow and pressure optimisation of a PEM fuel cell range extender system

In order to eliminate the local CO₂ emissions from vehicles and to combat the associated climate change, the classic internal combustion engine can be replaced by an electric motor. The two most advantageous variants for the necessary electrical energy storage in the vehicle are currently the purely electrochemical storage in batteries and the chemical storage in hydrogen with subsequent conversion into electrical energy by means of a fuel cell stack. The two variants can also be combined in a battery electric vehicle with a fuel cell range extender, so that the vehicle can be refuelled either purely electrically or using hydrogen. The air compressor, a key component of a PEM fuel cell system, can be operated at different air excess and pressure ratios, which influence the stack as well as the system efficiency. To asses the steady state behaviour of a PEM fuel cell range extender system, a system test bench utilising a commercially available 30 kW stack (96 cells, 409 cm² cell area) was developed. The influences of the operating parameters (air excess ratio 1.3 to 1.7, stack temperature 20 °C–60 °C, air compressor pressure ratio up to 1.67, load point 122 mA/cm² to 978 mA/cm²) on the fuel cell stack voltage level (constant ambient relative humidity of 45%) and the corresponding system efficiency were measured by utilising current, voltage, mass flow, temperature and pressure sensors. A fuel cell stack model was presented, which correlates closely with the experimental data (0.861% relative error). The air supply components were modelled utilising a surface fit. Subsequently, the system efficiency of the validated model was optimised by varying the air mass flow and air pressure. It is shown that higher air pressures and lower air excess ratios increase the system efficiency at high loads. The maximum achieved system efficiency is 55.21% at the lowest continuous load point and 43.74% at the highest continuous load point. Future work can utilise the test bench or the validated model for component design studies to further improve the system efficiency.     

The control strategy for a molten carbonate fuel cell hybrid system

Based on mathematical modelling and numerical simulations, the control strategy for a molten carbonate fuel cell hybrid system (MCFC-HS) is presented. Adequate maps of performances with three independent parameters are shown. The independent parameters are as follows: stack current, fuel mass flow and compressor outlet pressure. Those parameters can be controlled by external load, fuel valve and turbine–compressor shaft speed, respectively.     

Development and analysis of novel six-lobe helical rotors for hydrogen fuel cell vehicle roots blowers

This paper suggests a novel six-lobe Roots profile to improve the performance of Roots blowers in hydrogen fuel cell vehicles. Mathematical models for rotor profile generation and geometric characteristics are established. A working process simulation model for Roots blowers is developed based on the lumped parameter method and is verified by experimental results. The key profile parameters are discussed and optimized in views of geometric and thermodynamic performance. Case studies are conducted to reveal the detailed performance map difference between several design cases. Results show that a trade-off exists between the rotor cavity volume and adiabatic indicated efficiency for Roots blowers. The proposed profile broadens the design space of rotors in tooth height and achieves a flexible adjustment for the leakage through the blow-hole and contact line. As a consequence, compared to conventional Roots profiles, the proposed rotor profile achieves higher adiabatic indicated efficiency under the same rotor cavity volume.     

An impedance-based predictive control strategy for the state-of-health of PEM fuel cell stacks

This work presents a control strategy for PEM fuel cell systems based on simultaneous impedance measurements on single cells. This control strategy distinguishes between flooding and drying of the cells in a stack and helps to run the stack at an optimal operating point. In the presented experiments, it has been found that impedance measurements can detect flooding phenomena in single cells minutes before they can be seen in related polarisation curves. It is shown that impedance measurements at two specific frequencies, one high and one low frequency impedance, are sufficient to predict voltage drops caused by flooding and drying. In flooding mode, the imaginary part of the low frequency impedance changes while the high frequency impedance remains stable and vice versa in drying mode. This technique reduces measuring time compared to the measurement of whole impedance spectra, without losing important information for the control of the system.