Intelligent uninterruptible power supply system with back-up fuel cell/battery hybrid power source

This paper presents the development of an intelligent uninterruptible power supply (UPS) system with a hybrid power source that comprises a proton-exchange membrane fuel cell (PEMFC) and a battery. Attention is focused on the architecture of the UPS hybrid system and the data acquisition and control of the PEMFC. Specifically, the hybrid UPS system consists of a low-cost 60-cell 300 W PEMFC stack, a 3-cell lead–acid battery, an active power factor correction ac–dc rectifier, a half-bridge dc–ac inverter, a dc–dc converter, an ac–dc charger and their control units based on a digital signal processor TMS320F240, other integrated circuit chips, and a simple network management protocol adapter. Experimental tests and theoretical studies are conducted. First, the major parameters of the PEMFC are experimentally obtained and evaluated. Then an intelligent control strategy for the PEMFC stack is proposed and implemented. Finally, the performance of the hybrid UPS system is measured and analyzed.     

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.     

Dynamic behaviour of Li batteries in hydrogen fuel cell power trains

A Li ion polymer battery pack for road vehicles (48 V, 20 Ah) was tested by charging/discharging tests at different current values, in order to evaluate its performance in comparison with a conventional Pb acid battery pack. The comparative analysis was also performed integrating the two storage systems in a hydrogen fuel cell power train for moped applications. The propulsion system comprised a fuel cell generator based on a 2.5 kW polymeric electrolyte membrane (PEM) stack, fuelled with compressed hydrogen, an electric drive of 1.8 kW as nominal power, of the same typology of that installed on commercial electric scooters (brushless electric machine and controlled bidirectional inverter). The power train was characterized making use of a test bench able to simulate the vehicle behaviour and road characteristics on driving cycles with different acceleration/deceleration rates and lengths. The power flows between fuel cell system, electric energy storage system and electric drive during the different cycles were analyzed, evidencing the effect of high battery currents on the vehicle driving range. The use of Li batteries in the fuel cell power train, adopting a range extender configuration, determined a hydrogen consumption lower than the correspondent Pb battery/fuel cell hybrid vehicle, with a major flexibility in the power management.     

Power assisted fuel cell

A hybrid fuel cell demonstrated pulse power capability at pulse power load simulations synonymous with electronics and communications equipment. The hybrid consisted of a 25.0 W Proton Exchange Membrane Fuel Cell (PEMFC) stack in parallel with a two-cell lead-acid battery. Performance of the hybrid PEMFC was superior to either the battery or fuel cell stack alone at the 18.0 W load. The hybrid delivered a flat discharge voltage profile of about 4.0 V over a 5 h radio continuous transmit mode of 18.0 W.     

Fuel cell system with sodium borohydride as hydrogen source for unmanned aerial vehicles

In this study, we design and fabricate a fuel cell system for application as a power source in unmanned aerial vehicles (UAVs). The fuel cell system consists of a fuel cell stack, hydrogen generator, and hybrid power management system. PEMFC stack with an output power of 100 W is prepared and tested to decide the efficient operating conditions; the stack must be operated in the dead-end mode with purge in order to ensure prolonged stack performance. A hydrogen generator is fabricated to supply gaseous hydrogen to the stack. Sodium borohydride (NaBH₄) is used as the hydrogen source in the present study. Co/Al₂O₃ catalyst is prepared for the hydrolysis of the alkaline NaBH₄ solution at room temperature. The fabricated Co catalyst is comparable to the Ru catalyst. The UAV consumes more power in the takeoff mode than in the cruising mode. A hybrid power management system using an auxiliary battery is developed and evaluated for efficient energy management. Hybrid power from both the fuel cell and battery powers takeoff and turning flight operations, while the fuel cell supplies steady power during the cruising flight. The capabilities of the fuel-cell UAVs for long endurance flights are validated by successful flight tests.     

Characterization and experimental results in PEM fuel cell electrical behaviour

A control oriented electrochemical static model of a proton exchange membrane fuel cell (PEMFC) stack is developed in this paper. Even though its validation is performed on a specific 7-cell PEMFC stack fed by humidified air and pure hydrogen, the methodology and fit parameters can be applied to different fuel cell systems with minor changes. The fuel cell model was developed combining theoretical considerations and semi-empirical analysis based on the experimental data. The proposed model can be successfully included into a larger dynamic subsystem to complete the power generation system.     

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.     

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.     

Hybrid systems with lead–acid battery and proton-exchange membrane fuel cell

Hybrid systems, based on a lead–acid battery and a proton-exchange membrane fuel cell (PEMFC) give the possibility to combine the advantages of both technologies. The benefits for different applications are discussed and the practical realisation of such systems is shown. Furthermore a numerical model for such a hybrid system is described and results are shown and discussed. The results show that the combination of lead–acid batteries and PEMFC shows advantages in case of applications with high peak power requirements (i.e. electric scooter) and applications where the fuel cell is used as auxiliary power supply to recharge the battery. The high efficiency of fuel cells at partial load operation results in a good fuel economy for recharging of lead–acid batteries with a fuel cell system.     

Experimental investigation on the dynamic performance of a hybrid PEM fuel cell/battery system for lightweight electric vehicle application

A hybrid system combining a 2 kW air-blowing proton exchange membrane fuel cell (PEMFC) stack and a lead–acid battery pack is developed for a lightweight cruising vehicle. The dynamic performances of this PEMFC system with and without the assistance of the batteries are systematically investigated in a series of laboratory and road tests. The stack current and voltage have timely dynamic responses to the load variations. Particularly, the current overshoot and voltage undershoot both happen during the step-up load tests. These phenomena are closely related to the charge double-layer effect and the mass transfer mechanisms such as the water and gas transport and distribution in the fuel cell. When the external load is beyond the range of the fuel cell system, the battery immediately participates in power output with a higher transient discharging current especially in the accelerating and climbing processes. The DC–DC converter exhibits a satisfying performance in adaptive modulation. It helps rectify the voltage output in a rigid manner and prevent the fuel cell system from being overloaded. The dynamic responses of other operating parameters such as the anodic operating pressure and the inlet and outlet temperatures are also investigated. The results show that such a hybrid system is able to dynamically satisfy the vehicular power demand.     

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.     

An actively controlled fuel cell/battery hybrid to meet pulsed power demands

This paper presents the experimental results of an actively controlled fuel cell/battery hybrid power source topology that can be widely used in many applications, such as portable electronic devices, communication equipment, spacecraft power systems, and electric vehicles, in which the power demand is impulsive rather than constant. A step-down DC/DC power converter is incorporated to actively control the power flow between the fuel cell and the battery to achieve both high power and high energy densities. The results show that the hybrid power source can achieve much greater specific power and power density than the fuel cell alone. This paper first demonstrates that an actively controlled hybrid with a 35 W hydrogen-fueled polymer electrolyte membrane fuel cell and a lithium-ion battery pack of six cells yielded a peak power of 100 W, about three times as high as the fuel cell alone can supply, while causing a very limited (10%) weight increase to the whole system. After that, another hybrid source using a different battery array (eight cells) was investigated to further validate the control strategy and to show the flexibility and generality of the hybrid source design. The experimental data show that the hybrid source using an eight-cell battery supplied a peak power of 135 W, about four times that of the fuel cell alone. Finally, three power sources including the fuel cell alone and the two hybrids studied were compared in terms of specific power, power density, volume, weight, etc. The design presented here can be scaled to larger or smaller power capacities for a variety of applications.     

Control strategy of a fuel-cell power module for electric forklift

Fuel cell-battery hybrid systems for the powertrain, which have the advantage of emission-free power generation and adapt to material transport and emission reduction, are investigated. Based on the characteristics of the fuel cell system and the characteristics of the electric forklift truck powertrain system, this work defines the design principle of the control strategy to improve overall performance and economy. A simulation platform for fuel cell and electric vehicles has been established. The optimal performance of the fuel cell stack and the battery capacity were defined for the specific application. An energy control strategy was defined for different operating cycles and operating conditions. Model validation involved comparing simulation results with experimental data obtained during VDI60 test protocol. The main parameters that influence the forklift performance were defined and evaluated, such as energy loss, fuel cell operating conditions and different battery charging cycles. The optimal size of the fuel cell stack of 11 kW and the battery of 10 Ah was determined for the specific load profile with the proposed control strategy. The results obtained in this work forms the basis for an in-depth study of the energy management of fuel cell battery drive trains for forklift trucks.     

Demonstration and assessment of dynamic performance of a hybrid power system based electric passenger cart

Fuel cell (FC) technology is showing excellent promise for many applications ranging from portable devices to vehicular systems. A stand-alone FC may not always satisfy the fast and transient load demands of a vehicular power system. As a result, FC units are usually hybridized with supplementary sources to meet the total power demand of the vehicle. In this paper, the energy demands of a light vehicle (a passenger cart) is developed using a hybrid power supply system involving a photovoltaic (PV) panel, a proton exchange membrane fuel cell (PEMFC) and a battery based energy storage system (ESS). In addition, the details of the physical construction of the modified hybrid cart are given. The most critical feature of an energy management strategy for a multiple-source based hybrid vehicle is the sharing of fast and transient load demands among the available power sources. For this purpose, a 300-s drive cycle is created in this paper to test the effectiveness of the load sharing strategy between FC, battery pack and PV panel. It is found that PEMFC dominates slow and moderate dynamic behaviors of the vehicle, while fast response of the battery group governs the rapid dynamic behaviors. The results also show that the integrating PV panel contributes noticeably to the dynamic behaviors of the system. Furthermore, a control-oriented simulation model for a PEMFC unit is verified with experimental data to test the success of the proposed technique.     

Experimental evaluation of a passive fuel cell/battery hybrid power system for an unmanned ground vehicle

Unmanned vehicles are increasing the performance of monitoring and surveillance in several applications. Endurance is a key issue in these systems, in particular in electric vehicles, powered at present mainly by batteries. Hybrid power systems based on batteries and fuel cells have the potential to achieve high energy density and specific energy, increasing also the life time and safe operating conditions of the power system. The objective of this research is to analyze the performance of a passive hybrid power system, designed and developed to be integrated into an existing Unmanned Ground Vehicle (UGV). The proposed solution is based on six LiPo cells, connected in series, and a 200 W PEM fuel cell stack, directly connected in parallel to the battery without any limitation to its charge. The paper presents the characterization of the system behavior, and shows the main results in terms of performance and energy management.     

Control design and power management of a stationary PEMFC hybrid power system

This paper develops robust control and power management strategies for a 6 kW stationary proton exchange membrane fuel cell (PEMFC) hybrid power system. The system consists of two 3 kW PEMFC modules, a Li–Fe battery set, and electrical components to form a parallel hybrid power system that is designed to supply uninterruptible power to telecom base stations during power outages. The study comprises three parts: PEMFC control, power management, and system integration. First, we apply robust control to regulate the hydrogen flow rates of the PEMFC modules in order to improve system stability, performance, and efficiency. Second, we design a parallel power train that consists of two PEMFC modules and one Li–Fe battery set for the uninterruptible power supply (UPS) requirement. Lastly, we integrate the system for experimental verification. Based on the results, the proposed robust control and power management are deemed effective at improving the stability, performance, and efficiency of the stationary power system.     

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.     

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.     

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.     

Development of integrated fuel cell hybrid power source for electric forklift

A hybrid drivetrain comprising a 16 kW polymer electrolyte membrane fuel cell system, ultracapacitor modules and a lead-acid battery was constructed and experimentally tested in a real counterweight forklift application. A scaled-down version of the hybrid system was assembled and tested in a controlled laboratory environment using a controllable resistive load. The control loops were operating in an in-house developed embedded system. The software is designed for building generic control applications, and the source code has been released as open source and made available on the internet. The hybrid drivetrain supplied the required 50 kW peak power in a typical forklift work cycle consisting of both loaded and unloaded driving, and lifting of a 2.4 tonne load. Load variations seen by the fuel cell were a fraction of the total current drawn by the forklift, with the average fuel cell power being 55% of nominal rating. A simple fuel cell hybrid model was also developed to further study the effects of energy storage dimensioning. Simulation results indicate that while a battery alone significantly reduces the load variations of the fuel cell, an ultracapacitor reduces them even further. Furthermore, a relatively small ultracapacitor is enough to achieve most of the potential benefit.