Power management system for a fuel cell/battery hybrid vehicle incorporating fuel cell and battery degradation

Optimization of fuel cell/battery hybrid vehicle systems has primarily focused on reducing fuel consumption. However, it is also necessary to focus on fuel cell and battery durability as inadequate lifespan is still a major barrier to the commercialization of fuel cell vehicles. Here, we introduce a power management strategy which concurrently accounts for fuel consumption as well as fuel cell and battery degradation. Fuel cell degradation is quantified using a simplified electrochemical model which provides an analytical solution for the decay of the electrochemical surface area (ECSA) in the fuel cell by accounting for the performance loss due to transient power load, start/stop cycles, idling and high power load. The results show that the performance loss based on remaining ECSA matches well with test data in the literature. A validated empirical model is used to relate Lithium-ion battery capacity decay to C-rate. Simulations are then conducted using a typical bus drive cycle to optimize the fuel cell/battery hybrid system. We demonstrate that including these degradation models in the objective function can effectively extend the lifetime of the fuel cell at the expense of higher battery capacity decay resulting in a lower average running cost over the lifetime of the vehicle.     

Energy management of PEM fuel cell/ supercapacitor hybrid power sources for an electric vehicle

This paper presents the utilization of a supercapacitor (SC) as an auxiliary power source in an electric vehicle (EV), composed of a proton electrolyte membrane fuel cell (PEMFC) as the main energy source. The main weak point of PEMFC is slow dynamics because one must limit the fuel cell current slope in order to prevent fuel starvation problems, to improve its performance and lifetime. The very fast power response and high specific power of a supercapacitor can complement the slower power output of the main source to produce the compatibility and performance characteristics needed in a propulsion system. DC-DC converters connected to the hybrid source ensure a constant voltage value in inverters inputs. After an architecture presentation of the hybrid energy source, two parallel-type configurations are explored in more detail. For each of them, the energy flow control and management, validated simulation shows the performance obtained in this configuration. The hybrid source management is based primarily on the intervention of the supercapacitor in fugitives' schemes such as slopes, different speeds and rapid acceleration. Secondly, the PEMFC intervenes to guarantee the power in permanent regime. Finally, simulation results considering energy management are presented and illustrated the hybrid energy source benefits.     

Fuel cell/supercapacitor passive configuration sizing approach for vehicular applications

Active configuration i.e., source coupling via a power converter, is the most common configuration for fuel cell/supercapacitor (FC/SC) vehicles. Passive connection of the FC with the SCs without any converters is an original and less expensive solution to distribute the power among the sources. This passive configuration does not require an energy management strategy. In fact, the power distribution only depends on the FC and SC impedance characteristics. Conventional methods to size the SC follow two criteria: storage capacity and maximum voltage. In this paper, a third criterion is added which is the FC operating current dynamics. This novel sizing methodology reduces the FC degradation and improves the global system efficiency. Experimental results provide validation to the proposed sizing approach. The SCs boost the FC to meet the requirements of the load with a guarantee of system stability reaching higher global performances and less stress to the FC.     

A wavelet-fuzzy logic based energy management strategy for a fuel cell/battery/ultra-capacitor hybrid vehicular power system

Due to increasing concerns on environmental pollution and depleting fossil fuels, fuel cell (FC) vehicle technology has received considerable attention as an alternative to the conventional vehicular systems. However, a FC system combined with an energy storage system (ESS) can display a preferable performance for vehicle propulsion. As the additional ESS can fulfill the transient power demand fluctuations, the fuel cell can be downsized to fit the average power demand without facing peak loads. Besides, braking energy can be recovered by the ESS. This study focuses on a vehicular system powered by a fuel cell and equipped with two secondary energy storage devices: battery and ultra-capacitor (UC). However, an advanced energy management strategy is quite necessary to split the power demand of a vehicle in a suitable way for the on-board power sources in order to maximize the performance while promoting the fuel economy and endurance of hybrid system components. In this study, a wavelet and fuzzy logic based energy management strategy is proposed for the developed hybrid vehicular system. Wavelet transform has great capability for analyzing signals consisting of instantaneous changes like a hybrid electric vehicle (HEV) power demand. Besides, fuzzy logic has a quite suitable structure for the control of hybrid systems. The mathematical and electrical models of the hybrid vehicular system are developed in detail and simulated using MATLAB^®, Simulink^® and SimPowerSystems^® environments.     

Intensifying vehicular proton exchange membrane fuel cells for safer and durable,design and operation

The explosion in a proton exchange membrane fuel cell (PEMFC) powered forklift in Louisiana, USA in May 2018 and the resulting fatality highlights the need for the improved safety of this technology. Apart from the safety concerns, PEMFC durability has been an important issue towards its further commercialization. Both the safety and durability concerns associated with this technology can be attributed to the temporal degradation of its components. In this study, we have developed a mathematical model that relates the microscale PEMFC degradation to the probability of a macroscale explosion in a Fuel Cell Electric Vehicle (FCEV). Using the model and the inherent safety principle of intensification, it was observed that increasing the operating temperature of the PEMFC system can significantly improve both its safety and durability while intensifying membrane design parameters i.e. membrane thickness and membrane conductivity do not provide any significant improvements. A key inference from this study is that the durability (expressed in voltage loss) and safety (expressed in explosion probability) of a PEMFC system are not perfectly correlated.     

Design modeling of lithium-ion battery performance

A computer design modeling technique has been developed for lithium-ion batteries to assist in setting goals for cell components, assessing materials requirements, and evaluating thermal management strategies. In this study, the input data for the model included design criteria from Quallion, LLC for Gen-2 18650 cells, which were used to test the accuracy of the dimensional modeling. Performance measurements on these cells were done at the electrochemical analysis and diagnostics laboratory (EADL) at Argonne National Laboratory. The impedance and capacity related criteria were calculated from the EADL measurements. Five batteries were designed for which the number of windings around the cell core was increased for each succeeding battery to study the effect of this variable upon the dimensions, weight, and performance of the batteries. The lumped-parameter battery model values were calculated for these batteries from the laboratory results, with adjustments for the current collection resistance calculated for the individual batteries.     

Modeling thermal management of lithium-ion PNGV batteries

Batteries were designed with the aid of a computer modeling program to study the requirements of the thermal control system for meeting the goals set by the Partnership for a New Generation of Vehicles (PNGV). The battery designs were based upon the lithium-ion cell composition designated Gen-2 in the US Department of Energy Advanced Technology Development Program. The worst-case cooling requirement that would occur during prolonged aggressive driving was estimated to be 250 W or about 5 W per cell for a 48-cell battery. Rapid heating of the battery from a very low startup temperature is more difficult than cooling during driving. A dielectric transformer fluid is superior to air for both heating and cooling the battery. A dedicated refrigeration system for cooling the battery coolant would be helpful in maintaining low temperature during driving. The use of ample insulation would effectively slow the battery temperature rise when parking the vehicle in warm weather. Operating the battery at 10 °C during the first several years when the battery has excess power would extend the battery life.     

Improvement of ultracapacitors-energy usage in fuel cell based hybrid electric vehicle

Hybrid electric power systems based on fuel cell stack and energy storage sources like batteries and ultracapacitors are a plausible solution to vehicle electrification due to their balance between acceleration performance and range. Having a high degree of hybridization can be advantageous, considering the different characteristics of the power sources. Some parameters to be considered are: specific power and energy, energy and power density, lifetime, cost among others. Ultracapacitors (UC) are of particular interest in electric vehicle applications due to its high-power capability, which is commonly required during acceleration. UCs are commonly used without a power electronics interface due to the high-power processing requirement. Although connecting UCs directly to the DC bus, without using a power converter, presents considerable advantages, the main disadvantage is related to the UC energy-usage capability, which is limited by constant DC bus control. This paper proposes a novel energy-management strategy based on a fuzzy inference system, for fuel-cell/battery/ultracapacitor hybrid electric vehicles. The proposed strategy is able to control the charge and discharge of the UC bank in order to take advantage of its energy storage capability. Experimental results show that the proposed strategy reduces the waste of energy due to dynamic brake in 14%. This represents a reduction in energy consumption from 218 Wh/km to 192 Wh/km for the same driving conditions. By using the proposed energy management strategy, the estimated fuel efficiency in miles per gallon equivalent was also increase from 96 mpge to 109 mpge.     

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.     

Investigating electrical contact resistance losses in lithium-ion battery assemblies for hybrid and electric vehicles

Lithium-ion (Li-ion) batteries are favored in hybrid-electric vehicles and electric vehicles for their outstanding power characteristics. In this paper the energy loss due to electrical contact resistance (ECR) at the interface of electrodes and current-collector bars in Li-ion battery assemblies is investigated for the first time. ECR is a direct result of contact surface imperfections, i.e., roughness and out-of-flatness, and acts as an ohmic resistance at the electrode-collector joints. A custom-designed testbed is developed to conduct a systematic experimental study. ECR is measured at separable bolted electrode connections of a sample Li-ion battery, and a straightforward analysis to evaluate the relevant energy loss is presented. Through the experiments, it is observed that ECR is an important issue in energy management of Li-ion batteries. Effects of surface imperfection, contact pressure, joint type, collector bar material, and interfacial materials on ECR are highlighted. The obtained data show that in the considered Li-ion battery, the energy loss due to ECR can be as high as 20% of the total energy flow in and out of the battery under normal operating conditions. However, ECR loss can be reduced to 6% when proper joint pressure and/or surface treatment are used. A poor connection at the electrode-collector interface can lead to a significant battery energy loss as heat generated at the interface. Consequently, a heat flow can be initiated from the electrodes towards the internal battery structure, which results in a considerable temperature increase and onset of thermal runaway. At sever conditions, heat generation due to ECR might cause serious safety issues, sparks, and even melting of the electrodes.     

Designing, building, testing and racing a low-cost fuel cell range extender for a motorsport application

Imperial Racing Green is an undergraduate teaching project at Imperial College London. Undergraduate engineers have designed, built and raced hydrogen fuel cell hybrid vehicles in the Formula Zero and Formula Student race series. Imperial Racing Green has collaborated with its fuel cell partners to develop a 13 kW automotive polymer electrolyte membrane fuel cell (PEMFC) system. A team of undergraduate engineers were given a relatively modest budget and less than 8 months to design and assemble an operational high-power PEMFC system. The fuel cell system was designed to provide the average power required by the team's 2011 Formula Student entry. This paper presents the team's experience of developing and testing an automotive fuel cell system for a race application and plans for its future development and integration onto the vehicle.     

Power switch failures tolerance and remedial strategies of a 4-leg floating interleaved DC/DC boost converter for photovoltaic/fuel cell applications

In recent years, many researchers have proposed new DC/DC converters in order to meet the fuel cell requirements. The reliability of these DC/DC converters is crucial in order to guarantee the availability of fuel cell systems. In these converters, power switches ranked the most fragile components. In order to enhance the reliability of DC/DC converters, fuel cell systems have to include fault-tolerant topologies. Usually, dynamic redundancy is employed to make a fault-tolerant converter. Despite this kind of converter allows ensuring a continuity of service in case of faults, the use of dynamic redundancy gets back to increase the complexity of the converter. In order to cope with reliability expectations in DC/DC converters, floating interleaved boost converters seem to be the best solution. Indeed, they have much to offer for fuel cells and DC renewable energy sources (i.e. photovoltaic system), including reduced input current ripple and reliability in case of faults. Despite the offered benefits of this topology, operating degraded modes lead up to undesirable effects such as electrical overstress on components and input current ripple increasing. The aim of this paper is to carry out a thorough analysis of these undesirable effects and to propose remedial strategies to minimize them.     

Techno-economic and behavioural analysis of battery electric,hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system in the UK

This paper conducts a techno-economic study on hydrogen Fuel Cell Electric Vehicles (FCV), Battery Electric Vehicles (BEV) and hydrogen Fuel Cell plug-in Hybrid Electric Vehicles (FCHEV) in the UK using cost predictions for 2030. The study includes an analysis of data on distance currently travelled by private car users daily in the UK. Results show that there may be diminishing economic returns for Plug-in Hybrid Electric Vehicles (PHEV) with battery sizes above 20 kWh, and the optimum size for a PHEV battery is between 5 and 15 kWh. Differences in behaviour as a function of vehicle size are demonstrated, which decreases the percentage of miles that can be economically driven using electricity for a larger vehicle. Decreasing carbon dioxide emissions from electricity generation by 80% favours larger optimum battery sizes as long as carbon is priced, and will reduce emissions considerably. However, the model does not take into account reductions in carbon dioxide emissions from hydrogen generation, assuming hydrogen will still be produced from steam reforming methane in 2030.     

Electrochemical cell studies based on non-aqueous magnesium electrolyte for electric double layer capacitor applications

Performances of electric double layer capacitors (EDLCs) based on an activated carbon electrode with acetonitrile (ACN), propylene carbonate (PC), or a ternary electrolyte, i.e., PC:ethylene carbonate (EC):diethyl carbonate (DEC), at 1 mol dm⁻³ of magnesium perchlorate [Mg(ClO₄)₂] salt have been investigated. The electrochemical responses were studied by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge experiments at 25 °C in a three-electrode configuration. For a comparative evaluation, lithium perchlorate (LiClO₄) salt-based systems were also evaluated. All the observed results showed typical EDLC characteristics within the potential range between 0 and 1 V vs. an Ag/Ag⁺ reference electrode. The Mg-based systems exhibited similar or rather better performances than the corresponding Li-based electrolytes; in particular, the rate capability of Mg-based ACN and PC electrolytes was much better than the corresponding Li-based electrolytes, indicating the high accessibility and utility of activated carbon pores by solvated Mg ions.     

Review on health-conscious energy management strategies for fuel cell hybrid electric vehicles: Degradation models and strategies

Considering the overwhelming pressure on worldwide demand of fossil fuels and the climate change caused by air pollution, hybrid electric vehicles have seen a promising future thanks to the development of renewable energy sources. Among various kinds of energy sources that have been used in hybrid electric vehicles, lithium-ion battery and proton exchange membrane (PEM) fuel cell exist to be the most favorable ones owing to their high energy density and power density. However, the degradation issues of the energy sources tend to be neglected when designing the energy management strategies for the hybrid electric vehicles. Concerning existing literature, degradation modelling methods of lithium-ion batteries and PEM fuel cells are reviewed and the possibility of integrating them into health-conscious energy management is discussed. Besides, a variety of energy management strategies that have taken the influence of degradations into consideration are reviewed and classified. The contribution of this paper is to investigate the possibility of developing a health-conscious energy management strategy based on accurate estimation of degradation to improve the durability of the system.     

Safe lithium-ion battery with ionic liquid-based electrolyte for hybrid electric vehicles

A lithium-ion battery featuring graphite anode, LiFePO₄-C cathode and an innovative, safe, ionic liquid-based electrolyte, was assembled and characterized in terms of specific energy and power after the USABC-DOE protocol for power-assist hybrid electric vehicle (HEV) application. The test results show that the battery surpasses the energy and power goals stated by USABC-DOE and, hence, this safe lithium-ion battery should be suitable for application in the evolving HEV market.     

Research and development of on-board hydrogen-producing fuel cell vehicles

Combining with the characteristics of different types of electric vehicles, the on-board hydrogen-producing fuel cell vehicle design is adopted, which eliminates the problems about the high-pressure hydrogen storage and the hydrogenation process. The fuel cell is used as the main power source to drive the motor, and the lithium battery is used as the auxiliary power source to accelerate and recycle energy in order to meet the special requirements, like energy recovery, power and dynamic characteristics, of fuel cell vehicles. On the ADVISOR simulation platform based on MATLAB/Simulink environment, a hybrid drive model and a pure fuel cell drive model are built, and simulation and comparative analysis are performed. In the hybrid drive model, fuel cells and lithium batteries work in the highly efficient and safe operating areas respectively, and the output power of fuel cell has small fluctuations, improving energy utilization efficiency and extending the service life of the fuel cell. At the same time, the charge and discharge of the lithium battery can be effectively managed to ensure the safety of charging and prolong the service life of the lithium battery.     

ANFIS-MPPT control algorithm for a PEMFC system used in electric vehicle applications

Fuel cell has been considered as one of the optimistic renewable power technologies for the automotive applications. The output power of a fuel cell is immensely dependent on cell temperature and membrane water content. Hence, a maximum power point tracking controller is essentially required to extract the optimum power from the fuel cell stack. In this paper, an adaptive neuro-fuzzy inference system based maximum power point tracking controller is presented for 1.26 kW proton exchange membrane fuel cell system used in electric vehicle applications. In order to extract the optimum power, a high step-up boost converter is connected between the fuel cell and the BLDC motor. The duty cycle of the converter is controlled by using ANFIS reference model, so that the maximum power is delivered to the BLDC motor. The performance of the proposed controller is tested under normal operating conditions and also for sudden variations in the cell temperatures of the fuel cell. In addition to this, to analyze the effectiveness and tracking behaviour of the proposed controller, the results were compared with those obtained using the fuzzy logic controller. Compared to the fuzzy logic controller, the proposed ANFIS controller has increased the average DC link power by 1.95% and the average time taken to reach the maximum power point is reduced by 17.74%.     

A fuzzy logic based supervisory controller for an FC/UC hybrid vehicular power system

Depending on growing concerns on energy crises and environmental issues, fuel cell (FC) powered electrical vehicles are favored for possible substitute to conventional internal combustion engine (ICE) based vehicular systems. However, the typical power profile of an automobile motor consisting of transients is not suitable for the use of a sole FC system for vehicle propulsion. This shortcoming could be partly overcome by hybridization. Two potential benefits of combining an FC system with an energy storage unit, ultra-capacitor (UC) has been presented in this study. Firstly, the durability of the FC system could be improved because the additional energy source can fulfill the transient power demand fluctuations. Secondly, the ability of the energy storage source to recover braking energy enhances the fuel economy greatly. An important aspect in designing a hybrid power structure is to find a suitable control strategy that can manage the active power sharing and take advantage of the inherent scalability and robustness benefits of the hybrid system. An integrated procedure for mathematical modeling and power control strategy design for an FC/UC hybrid vehicle is presented in this paper. A fuzzy logic supervisory controller based power management strategy that secures the power balance in hybrid structure, enhances the FC performance and minimizes the power losses is proposed. The main contribution of this paper apart from the previous studies of the authors is the modeling of the complete FC power system with air supply compressor and the integration of the control of the FC system internal dynamics (especially the oxygen excess ratio) into the overall supervisory control structure to maximize the efficiency and durability. To demonstrate the effectiveness of the proposed power management scheme, simulation studies were performed using MATLAB^®, Simulink^® and SimPowerSystems^® environments by integrating the detailed mathematical and electrical models of the hybrid vehicular system.     

Comparative assessments of two integrated systems with/without fuel cells utilizing liquefied ammonia as a fuel for vehicular applications

In the current study, two different integrated systems for vehicular applications are presented and thermodynamically analyzed. The first system consists of liquefied ammonia tank, dissociation and separation unit (DSC) for decomposition of ammonia and an internal combustion engine (ICE) to power the vehicle. The second system is a hybrid system consisting of liquefied ammonia tank, DSC unit, a small ICE and a fuel cell system. In the second system, the main power unit is fuel cell and a supplementary internal combustion engines is also utilized. The exhaust gasses emitted from the ICE are used to provide the required heat for the thermal decomposition process of ammonia. The ICE is fueled with a mix of ammonia and hydrogen generated from the DSC unit that is installed in the two systems. Hydrogen generated from DSC unit will be utilized to operate fuel cell installed in system 2. The proposed systems are analyzed and assessed both energetically and exergetically. A comprehensive parametric study is carried out for comparative assessments to determine the influence of altering design and operating parameters such as the amount of ammonia fuel supplied to the two systems on the performance of the two systems. The overall energy and exergy efficiencies for system 1 and system 2 are found to be 61.89%, 63.34%, 34.73% and 38.44% respectively. The maximum exergy destruction rate in the two systems occurred in the ICE.