Fuel Cell-Based Powertrain Analysis for Tramway Systems

<div class="section abstract"> <div class="htmlview paragraph">The SAE J3211 procedure applies to squeal evaluation for foundation brakes using single-ended inertia dynamometers for friction couples used on vehicles with regenerative braking systems. This document applies to squeal noise occurrences for on-road passenger cars and light trucks with a gross vehicle weight rating of 4536 kg or below and with at least one rechargeable energy storage system as a source for propulsion. The procedure incorporates aspects related to (a) minimum inertia dynamometer capabilities, (b) fixture requirements and setup, and (c) test sequences with emphasis on brake temperatures, brake pressure profiles, and strategies to represent brake blending.</div> <div class="htmlview paragraph">For this document, squeal occurs when the peak noise level is at least 70 dB(A) between 1.25 and 16 kHz for tests using full suspension corners or complete axle assemblies, or between 2 and 16 kHz for brakes not using an entire suspension corner.</div> <div class="htmlview paragraph">Test facilities intending to use this document, building on their expertise in conducting SAE J2521, shall review in detail the changes to test parameters (mainly brake temperatures and brake pressures) for legacy modules.</div> <div class="htmlview paragraph">This document also applies to vehicles with electromechanical braking systems to actuate the foundation brake. The test requester and the test facility are responsible for converting the hydraulic pressure levels into their equivalent clamping forces for brakes using electromechanical actuation.</div> <div class="htmlview paragraph">Before using this document for chassis dynamometer testing, review in detail the specifics related to at least (a) instrumentation, including in-cabin microphones; (b) threshold levels for noise detection; (c) temperature control priority between the front and rear axles; (d) vehicle loading and load distribution; (e) cooling air and environmental conditioning; (f) detailed terminology and labeling of channels and sensors; and (g) the regenerative settings and the state of charge during the test.</div> <div class="htmlview paragraph">Before using this document along with other methods to recreate the regenerative brake blending (e.g., Software-in-the-Loop or Hardware-in-the-Loop), consider (a) the vehicle powertrain, blending architecture and its applicable models, (b) actual profiles intended to recreate (e.g., control strategies, state of charge, test scenarios), and (c) actual embodiment of the simulation and integration with the native controls of the brake dynamometer.</div> <div class="htmlview paragraph">This document does not include noise from other sources (e.g., parking brakes, electric machines, driveline components).</div> </div>

<div class="section abstract"><div class="htmlview paragraph">In the quest for reduced cost and shorter development times for fuel cell systems in industrial applications, two major issues arise. First, the electrochemical behavior of fuel cell systems is inherently difficult to predict. Second, testing fuel cell systems is resource intensive. These issues compound: Setting up an accurate model of a fuel cell system incurs long testing periods for model validation. Further, it does not guarantee acceptable results outside the tested range or for other membrane electrode assembly compositions.</div><div class="htmlview paragraph">To mitigate these two major issues an X in the Loop concept is proposed. Essentially, this is the direct integration of the test sample, here a single fuel cell, into the modelling environment of the whole system. In practice, two strategies with different levels of integration are defined.</div><div class="htmlview paragraph">The first strategy consists of initially deducing the operating parameters of the sample cell from the fuel cell system model. Then, setting them to the sample cell in the test bench. The response of the test sample is finally used to validate the designed system or update the parameters of the fuel cell model.</div><div class="htmlview paragraph">The second strategy is a step further towards the integration of the test sample into the model. Here, the core model of the fuel cell inside the fuel cell system model is completely replaced with the test sample, reducing the need for an accurate electrochemical model while improving the prediction of the behavior of the fuel cell system.</div><div class="htmlview paragraph">Compared to previously proposed testing concepts, here the balance of plants is directly integrated through a digital emulator, leading to a closer representation of the complete system. Furthermore, the test bench results are looped back to the model at run-time leading to a closer match between testing conditions and the real world as well a reduced impact of inaccuracies in the modelling of the fuel cell.</div><div class="htmlview paragraph">On the way to realizing this goal, an experimental test bench capable of showcasing working prototypes of the proposed operating strategies has been built.</div></div>

<div class="htmlview paragraph">In order to improve the fuel economy of city buses, which start and stop frequently, a system has been developed that stores braking energy in a hydraulic accumulator and uses the energy when the vehicle is in its start and acceleration modes.</div> <div class="htmlview paragraph">Through microcomputer control of the entire power train and energy storage system, the following goals are achieved: <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1.</span> <div class="htmlview paragraph">By applying currently available transmission technologies to the conventional power train system, all component functions are controlled so as to minimize the losses over the driving cycle.</div></li> <li class="list-item"> <span class="li-label">2.</span> <div class="htmlview paragraph">By applying a regenerative braking system, as much vehicle kinetic energy as possible is recovered and stored, and,</div></li> <li class="list-item"> <span class="li-label">3.</span> <div class="htmlview paragraph">The energy stored is used so as to achieve maximum overall efficiency.</div></li></ol></div> <div class="htmlview paragraph">A test vehicle functioning in city conditions achieved a 30% fuel economy gain.</div> <div class="htmlview paragraph">Other advantages of this system are that brake wear is greatly reduced and clutch life is significantly extended since the vehicle can start in motion using only hydraulic energy.</div>

<div class="htmlview paragraph">It is well known how local and global environment issues as well as the consumption and supply of energy are major challenges for the future of our planet.</div> <div class="htmlview paragraph">Just to give an example, transports in Europe today rely for 98% on oil.</div> <div class="htmlview paragraph">Internal combustion engines today are a major cause of global warming and local pollution that causes the closing of most city centres in Europe.</div> <div class="htmlview paragraph">Fuel cells have the potential to replace the conventional power generation technologies mainly promising efficiency improvements which could lead to energy saving and reduction of greenhouse gas emission.</div> <div class="htmlview paragraph">In 2001, CRF (FIAT research center) started together with Nuvera Fuel Cells europe Srl a project to evaluate the exploitation of FC inside the Seicento car, studying different levels of hybridisation: from an APU range extender to a full power fuel cell.</div> <div class="htmlview paragraph">The objective of this paper is to give an overview of the performance evolution of the fuel cell powertrain used in the Seicento prototypes and their integration inside the vehicle power plant. In particular the paper highlights the effectiveness and robustness of the system mainly related to the air and water management developed by CRF and NUVERA. The paper also reports comparison of the Seicento fuel cell vehicle with road testing results among different electric vehicles developed by CRF.</div>

<div class="section abstract"><div class="htmlview paragraph">Sustainable mobility is a pressing challenge for modern society. Electrification of transportation is a key step towards decarbonization, and hydrogen Fuel Cell Hybrid Electric Vehicles (FCHEVs) offer a promising alternative to Battery Electric Vehicles (BEVs), especially for long-range applications: they combine a battery system with a fuel cell, which provides onboard electric power through the conversion of hydrogen. Paramount importance is then given to the design and sizing of the hybrid powertrain for achieving a compromise between high performance, efficiency, and low cost.</div><div class="htmlview paragraph">This work presents a Hardware-in-the-Loop (HIL) platform developed for designing and testing the powertrain layout of an FCHEV. The platform comprises two systems: a simulation model reproducing the dynamics of a microcar and a hardware system for the fuel cell hybrid electric powertrain. The former simulates the vehicle's behavior, while the latter is composed of a 2kW real fuel cell stack and a 100Ah Li-ion battery pack. This element is used for real-time testing of the hybrid powertrain, using a programmable power supply that emulates the vehicle and motor load request.</div><div class="htmlview paragraph">Two fuel cell stack configurations have been analyzed by applying a linear scale-up approach (2kW and 4kW) and tested on an acceleration and deceleration driving cycle, representative of the microcar application; a simple fuzzy logic control strategy has been chosen for the test.</div><div class="htmlview paragraph">The system's performances have been evaluated and deeply analyzed in terms of component behavior and energy efficiency. The results demonstrate that the 4kW stack configuration scores a nearly 5% higher efficiency than the 2kW stack, mainly operating in the lower current regions corresponding to higher efficiencies. The improvements can then be translated into an increase in the vehicle's estimated range, more than balancing the increased weight burden of nearly 10kg. By enabling the possibility to consider and test the real behavior of powertrain components, the HIL platform has proven to be an effective tool for design purposes.</div></div>

<div class="htmlview paragraph">The modeling of the energy storage system (ESS) of a Hybrid Electric Vehicle (HEV) poses a considerable challenge. The problem is not amenable to physical modeling without simplifying assumptions that compromise the accuracy of such models. An alternative is to build conventional empirical models. Such models, however, are time-consuming to build and are data-intensive. In this paper, we demonstrate the application of an <b>artificial neural network</b> (ANN) to modeling the ESS. The model maps the system's state-of-charge (SOC) and the vehicle's power requirement to the bus voltage and current. We show that ANN models can accurately capture the complex, non-linear correlations accurately. Further, we propose and deploy our new technique, <b>Smart Select</b>, for designing ANN training data. The underlying philosophy of Smart Select is to design the training data set such that it is uniformly distributed over the entire range of an appropriate ANN output variable, which is typically the variable that is most difficult to model. In this case, we selected training data that were uniformly distributed over the current range. We show that smart-select is economical in comparison with conventional techniques for selection of training data. Using this technique and our in-house ANN software (the CUANN“), we developed an artificial neural network model (inputs=2, hidden neurons=3, outputs=2) utilizing only 1583 of the available 32,254 points. When validated on the remaining points, its predictive accuracy, measured by R-squared error, was 0.9978. Next, we describe the integration of the ANN model of the ESS into the MATLAB-SIMULINK environment of NREL's vehicle simulation software, ADVISOR. This yields a simpler implementation of the ESS module in ADVISOR and does away with certain tenuous assumptions in the original implementation.</div> <div class="htmlview paragraph">Lastly, we also show how a dramatic reduction in the size of the training data set may be obtained by applying the <b>model modifier approach</b> developed by our research group at the University of Colorado at Boulder.</div>

<div class="htmlview paragraph">The increase of the electrical power required by current vehicles suggests the need to evaluate its impact on fuel consumption, emissions and performances.</div> <div class="htmlview paragraph">Moreover, due to the growing amount of cars equipped with Air Conditioning System, a deep knowledge on how these additional loads influence vehicle performances is required.</div> <div class="htmlview paragraph">Often, the mechanical power requested by electrical and AC systems is comparable to the mechanical power necessary to move the vehicle (or sometimes even higher) and this happens mainly during urban driving cycles.</div> <div class="htmlview paragraph"><i>Drivetrain 3.0</i> is an integrated simulation model for vehicle energetic evaluation and management; fuel consumption and performances on a generic speed vs time driving cycle are dynamically evaluated as a function of electrical power loads and their possible management strategies.</div> <div class="htmlview paragraph">Other additional mechanical loads (i.e. climate compressor) and the related transmission efficiency could also be taken into account.</div> <div class="htmlview paragraph">Furthermore, <i>Drivetrain 3.0</i> can calculate the fuel consumption as a function of the state of charge (SOC) of the battery and the engine idle rpm boost (depending on the energy management strategies), in order to guarantee the electrical balance.</div> <div class="htmlview paragraph">The simulation model enables the evaluation of the effects of Start&Stop strategy on fuel consumption, taking into account the electrical power consumption when the engine is switched off.</div>

<div class="section abstract"><div class="htmlview paragraph">The performance of electrical vehicles strongly depends on characteristics of its energy storage system. A typical lithium-ion battery system is supervised by a battery management system to optimize operation and ensure safety over its whole lifecycle. Advanced battery management systems apply sophisticated fast charging procedures and active cell balancing. In future, impedance spectroscopy based on driving current stimulation for online estimation of the energy storage’s state of health can be expected. For efficient development and testing of such battery management systems it is impractical to use real lithium-ion cells in arbitrary condition of state of charge, temperature and state of health. Consequently, hardware in the loop cell emulators are state of the art. Most of them are limited to low frequency operation. In this paper, a novel modular wide bandwidth high performance lithium-ion cell emulator is introduced. The performance is proven by applying a commercial active cell balancing system and by performing electrochemical impedance spectroscopy. One electronic unit emulates a single cell, while multiple of them can be stacked to form a complete energy storage system up to 1000 V. Every module is autonomously operating in stand-alone mode and contains the full computing power for emulating open circuit voltage and output impedance depending on state of charge, temperature and aging. A fast high resolution acquisition stage samples the input current with 18 bit at 5 MSPS. The output cell voltage is generated by a power amplifier with 8 MHz bandwidth and up to ±10 A output current, while the output is fully protected. Leakage current can be measured down to 1 μA. High performance and long term stability is achieved by a self-calibrating system, using one single stable floating Zener reference.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In the future, conventional powertrains will increasingly be supplied by sustainable energy sources. Long-haul freight transport requires efficient energy storage and the ability to refuel quickly. For this reason, hydrogen-powered PEM fuel cells are being discussed as a future energy source for long-distance vehicles. However, there are numerous challenges in packaging, system cooling and service life. Above all, the dissipation of the fuel cell’s heat losses places high demands on the design of the cooling system due to the relatively low operating temperature.</div><div class="htmlview paragraph">In the presented study, a complete generic drive train of a long-distance commercial vehicle was set up within a suitable simulation environment to investigate the required sizes of the fuel cell stack, the HV battery, the hydrogen tanks, and the cooling circuit. The thermodynamic and electrochemical data that was necessary to describe the stack, the BoP components, the battery, the coolers, and the drivetrain components were taken from the literature or similar applications.</div><div class="htmlview paragraph">Afterward, the requested propulsion power, fuel consumption, and cooling demand were analyzed for constant vehicle speed and representative driving cycles. Mountainous highway passages, as typically occurring in the Alpes, were investigated for different ambient temperatures. Detailed loss analyses were carried out for the whole powertrain and visualized in Sankey diagrams.</div><div class="htmlview paragraph">The results revealed challenging thermal management at high ambient temperatures that may result in degrading fuel cell power when crawling uphill with low vehicle speed. However, the potential and suitability of PEM fuel cells for sustainable long-haul transport could be clearly demonstrated.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Lithium battery technology currently dominates the electrical vehicle market and it is expected will dominate over the next decade as it is mature enough to rapidly deliver new electrochemical devices. However, several issues related to safety and large scale availability of Lithium have determined in recent years the development of a new research field, known as "beyond Lithium", in the attempt to identify innovative systems for electric energy storage based on different metal anodes. In this context, metal-air batteries are the most promising electrochemical devices able to provide high theoretical energy and power densities and also, if properly conceived, to satisfy the sustainability characteristics imposed by modern legislations. Among the various metals considered as anode in metal-air batteries, Aluminum is the material with the most satisfactory parameters of economy/ecology and electrochemistry at the same time. The technological challenge in the research on Al-air batteries consists in obtaining sustainable electrochemical devices with practical values of energy and power density, that are competitive with those of current lithium-ion systems. Above all, to make these batteries electrically rechargeable in aqueous electrolytes, taking into account that the re-deposition of the Aluminum during the charging phase is hampered by competitive reactions which consume current before the reduction potential of aluminum is reached.</div><div class="htmlview paragraph">In this paper we present our recent results on quasi-solid-state Aluminum-air batteries realized with new electrolytes based on aqueous solutions at different pH and natural polysaccharides. We show that gel solid electrolytes in primary Al-air cells are able to provide 70 mAh cm<sup>-2</sup> as cell capacity at discharge current of 10 mA cm<sup>-2</sup>. We finally remark some differences between alkaline and acidic electrolytes and their impact on primary cell electrochemical performance.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Hybrid powertrains are replacing conventional combustion drives at an accelerating rate, while offering a reduction in fuel consumption and toxic exhaust emissions. The large share of hybrid solutions in engine vehicles has been observed for the compact class and in SUVs. The Authors of this study proposed an energy flow assessment in the hybrid powertrain system of an SUV in various driving conditions: urban, extra-urban and motorway. The tests were performed in accordance with the stipulations of the RDC test conditions and its requirements. The tests were carried out on a Toyota RAV4 HEV equipped with a 2.5 dm<sup>3</sup> engine in a hybrid drive system along with Li-Ion batteries, which had an energy capacity of 1.11 kWh (4.3 Ah). The research was carried out on an urban route in Poznan as well as in its vicinity using three drive modes of the drive system: Eco, Normal and Sport. Based on the results of energy flow tests, it was found that, regardless of the initial state of charge (SOC) of battery, the vehicle would reach constant SOC values in the second phase of the test - in the extra-urban driving phase. Such conditions stabilize after about 30 km of urban driving. The differences in the range of these SOC values were around 10%. Due to the conditions of motorway driving, the SOC changes were very small and amounted to about 3-5% while covering about 20 km (in this driving mode). The tests confirmed the slight influence that the driving mode (eco, normal, sport) had on the final measured charge values: for discharge, charging or regeneration. The share of time operating in electric mode for individual test phases was also determined, and it was approximately 65-68%, 25-30% and 5-8% in the urban, extra-urban and motorway phases, respectively.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The linear internal combustion engine-linear generator integrated system (LICELGIS) is a generating unit with high power density, high efficiency and low emission for the range-extended electric vehicle. The LICELGIS starts with the linear generator, which shows the advantages of speed, efficiency and emission reduction, as well as the prerequisite to guarantee the steady operation of the system.</div><div class="htmlview paragraph">This paper focuses on the reversing control method and the energy utilization efficiency in the starting process of the LICELGIS.</div><div class="htmlview paragraph">Pursuant to the starting requirements of the linear internal combustion engine, the fewest driving cycle and the evaluation index are obtained. Meanwhile, the velocity tracking mode and the position tracking mode is proposed for the control of the starting force reversing. The motions of the starting process under two control method are comparatively analyzed, indicating that the former has a high efficiency, while the latter is more likely to achieve.</div><div class="htmlview paragraph">The starting process of the LICELGIS is simulated on the validated mathematical model with the position tracking mode to analyze the impact of the different starting parameters including the initial position, the magnitude of starting force, and the reversing position of the starting force.</div><div class="htmlview paragraph">An improved position tracking mode with variable reversing positions is proposed, synthesized both the features of the velocity tracking mode and the position tracking mode. The reversing positions of the starting force each cycle are determined by what under the velocity tracking mode. This optimized method can be the scheme for the starting experiment of the system prototype.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Current hybrid and electric powertrains in Class 1 through to Class 7 vehicle segments, are still disadvantaged by very low market penetration due to high procurement and operational cost barriers which have increased the gap between the technology experience and the expected benefits of powertrain electrification.</div><div class="htmlview paragraph">Fundamentally, baseline gasoline and diesel vehicles with over 100 years of established supply chain network and manufacturing economies of scale, have made it difficult for hybrid and electric alternatives to compete even with the continuous drop in price of these new technologies and numerous government incentives.</div><div class="htmlview paragraph">A new approach is proposed in this segment with an Integrated Torque Assist Transmission (ITAT) that addresses the typical fuel inefficiency challenges of the baseline powertrains where mostly up to 12% of their fuel content is used for actual vehicle propulsion while the rest is lost to heat dissipation. The new ITAT replaces the stock transmission as an electrification upgrade with the choice of a Battery or Ultracap energy storage system of 48V or 300V specification. The transmission system can be retrofitted as an aftermarket upgrade or installed on the assembly line.</div><div class="htmlview paragraph">A model cargo van is used to demonstrate the benefits of the torque assist transmission approach which includes engine downsizing if applicable or better fuel economy from the stock engine if it is retained as well as the cost benefit of over 60% off the shelf component sourcing using most of the existing supply chain and manufacturing infrastructure.</div></div>

<div class="htmlview paragraph">While the ZEV program's electric vehicles did not become successful market-driven products, many of the technical advantages of electric vehicles were validated by enthusiastic California consumers. Yet, battery technology has been and continues to be the limiting factor in terms of cost, functionality (range) and durability of EV systems.</div> <div class="htmlview paragraph">The automotive industry has largely moved on to research and development of other approaches to extremely low emissions and reduced fossil fuel consumption. PZEV gasoline vehicles, Hybrid electric vehicles, clean (EPA Tier 2) diesel vehicles and Proton Exchange Membrane (PEM) fuel cell electric vehicles (FCEVs) are the focus of attention.</div> <div class="htmlview paragraph">The purpose of this paper is to explore another possible solution: a battery electric vehicle with a relatively small fuel cell auxiliary power unit (APU) to recharge the battery pack during driving. The attraction of this configuration is the use of a relatively small battery pack (to allow 65 - 110 km of ZEV range) while increasing vehicle range and functionality to be equivalent to conventional vehicles (400 - 650 km). Another key attraction is that a majority of km could be efficiently refueled from the grid allowing low or zero CO<sub>2</sub> power generating technology to be deployed in private transportation without the enormous cost and inefficiency of the H<sub>2</sub> infrastructure.</div> <div class="htmlview paragraph">The combination of Solid Oxide Fuel Cell (SOFC) APU and advanced Lithium Ion battery systems appears to make the fuel cell range extender EV an attractive system in terms of efficiency, weight and (in the midterm) cost. This paper will discuss the product attributes and advantages that such a system would bring to the customer and society and compare SOFC to Proton Exchange Membrane (PEM) fuel cell and other competing APU technologies. This paper will present system level assessment and analysis of the SOFC/Lithium Ion range extender EV applied to a GM EV1 platform.</div>

<div class="htmlview paragraph">Fuel cell hybrid vehicles (FCHVs) use an energy management strategy to partition the power supplied by the fuel cell and energy storage system (ESS). This paper presents an adaptive energy management strategy, created in the ADVISOR<sup>™</sup> software, for a series FCHV. The strategy uses a local or “real-time” optimization approach, which aims to reduce total energy consumption at each instantaneous time interval by dynamically adjusting the amount of power supplied by the fuel cell and ESS. Compared with a static control strategy, the adaptive strategy improved the simulated FCHV's fuel economy by 1.4%-8.5%, depending on the drive cycle.</div>