The batteries used in plug-in hybrid electric vehicles (PHEVs) need to overcome significant technical challenges in order for PHEVs to become economically viable and have a large market penetration. The internship at Argonne National Laboratory (ANL) involved two experiments which looked at a vehicle systems approach to analyze two such technical challenges: Battery life and low battery power at cold (-7 ⁰C) temperature. The first experiment, concerning battery life and its impact on gasoline savings due to a PHEV, evaluates different vehicle control strategies over a pre-defined vehicle drive cycle, in order to identify the control strategy which yields the maximum dollar savings (operating cost) over the life of the vehicle, when compared to a charge sustaining hybrid. Battery life degradation over the life of the vehicle, and fuel economy savings on every trip (daily) are taken into account when calculating the net present value of the gasoline dollars saved. The second experiment evaluates the impact of different vehicle control strategies in heating up the PHEV battery (due to internal ohmic losses) for cold ambient conditions. The impact of low battery power (available to the vehicle powertrain) due to low battery and ambient temperatures has been well documented in literature. The trade-off between the benefits of heating up the battery versus heating up the internal combustion engine are evaluated, using different control strategies, and the control strategy, which provided optimum temperature rise of each component, is identified.

La propulsion des véhicules électriques hybrides parallèles est généralement assurée par un moteur à combustion interne combiné à une machine électrique réversible. Les flux de puissance entre ces deux organes de traction sont déterminés par un algorithme de supervision, qui vise à réduire la consommation de carburant et éventuellement les émissions de certains polluants. Dans la littérature, la théorie de la commande optimale est maintenant reconnue comme étant un cadre puissant pour l’élaboration de lois de commande pour la gestion énergétique des véhicules full-hybrides. Ces stratégies, dénommée « Stratégies de Minimisation de la Consommation Equivalente » (ECMS) sont basée sur le principe du Maximum de Pontryagin. Pour démontrer l’optimalité de l’ECMS, on doit supposer que les limites du système de stockage ne sont pas atteintes durant le cycle de conduite. Il n’est plus possible de faire cette hypothèse lorsque l’on considère les véhicules micro et mild hybrides étudiés dans cette thèse car la variable d’état atteint généralement plusieurs fois les bornes. Des outils mathématiques adaptés à l’étude des problèmes de commande avec contraintes sur l’état sont présentés et appliqués à deux problèmes en lien avec la gestion énergétique. Le premier problème consiste à déterminer le profil optimal de la tension aux bornes d’un pack d’ultra-capacités. Le second problème se concentre sur un système électrique intégrant deux stockeurs. L’accent est mis sur l’étude des conditions d’optimalités valables lorsque les contraintes sur l’état sont actives. Les conséquences de ces conditions pour la commande en ligne sont mises en avant et exploitées afin de concevoir une commande en temps réel. Les performances sont évaluées à l’aide d’un prototype. Une comparaison avec une approche de type ECMS plus classique est également présentée. / Parallel hybrid electric vehicles are generally propelled by an internal combustion engine, which is combined to a reversible electric machine. The power flows between these two traction devices are determined by a supervisory control algorithm, which aims at reducing the fuel consumption and possibly some polluting emissions. In the literature, optimal control theory is now recognized as a powerful framework for the synthesis of energy management strategies for full hybrid vehicles. These strategies are referred to as “Equivalent Consumption Minimization Strategies” (ECMS) and are based on the Pontryagin Maximum Principle. To demonstrate the optimality of ECMS, it must be assumed that the storage system limits are not reached during the drive cycle. This hypothesis cannot be made anymore when considering the micro and mild hybrid vehicles studied in this thesis because the state variable generally reaches several times the boundaries. Some mathematical tools suitable for the study of state constrained optimal control problems are introduced and applied to two energy management problems. The first problem consists in determining the optimal profile of the voltage across a pack of ultra-capacitors. The second problem focuses on a dual storage system. The stress is put on the study of the optimality conditions holding in case of active state constraints. Some consequences of these conditions for the online control are pointed out are exploited for the design of a real-time controller. Its performances are assessed using a demonstrator vehicle. A comparison with a classical ECMS-based approach is also provided.

Die anspruchsvollen Zielsetzungen zum CO2-Ausstoß von Kraftfahrzeugen verlangen immer stärker nach hocheffizienten Fahrzeugkonzepten und werden zukünftig zu deutlich höheren Elektrifizierungsanteilen der Antriebe führen. Die große Herausforderung liegt dabei in der Lösung des Zielkonfliktes zwischen voll elektrischem Fahren und erstfahrzeugtauglicher Reichweite. Im Rahmen eines Forschungsprojektes zur Konzeption von Hybridfahrzeugen hat die BMW Forschung ein Konzeptfahrzeug entwickelt, das im urbanen Bereich emissionsfrei betrieben werden kann und dennoch alltagstauglich für spontane längere Fahrten nutzbar ist (Abbildung 1). Die für dieses Projekt abgeleiteten Ziele waren ein Verbrauch von < 2,5 l im Ladungserhaltungsbetrieb, eine E-Reichweite von 100 km, eine BMW-adäquate Beschleunigung von < 8 sec von 0 auf 100 km/h, eine erstfahrzeugtaugliche Höchstgeschwindigkeit von 180 km/h, ein Raumangebot auf Niveau heutiger viersitziger Coupés im Kompaktsegment und eine Gesamtreichweite von 1.000 km (Eiletz 2015a). Im Rahmen des Beitrags werden sowohl Prozess und Vorgehensweise bei der Gestaltung des Hocheffizienz-Konzeptfahrzeugs als auch die Ergebnisse des Forschungsprojektes dargelegt.

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<p>In this thesis, direct hydrogen Proton Exchange Membrane (PEM) fuel cell systems in vehicles are investigated through modelling, field tests and public acceptance surveys.</p><p>A computer model of a 50 kW PEM fuel cell system was developed. The fuel cell system efficiency is approximately 50% between 10 and 45% of the rated power. The fuel cell auxiliary system,<i> e.g.</i> compressor and pumps, was shown to clearly affect the overall fuel cell system electrical efficiency. Two hydrogen on-board storage options, compressed and cryogenic hydrogen, were modelled for the above-mentioned system. Results show that the release of compressed gaseous hydrogen needs approximately 1 kW of heat, which can be managed internally with heat from the fuel cell stack. In the case of cryogenic hydrogen, the estimated heat demand of 13 kW requires an extra heat source. </p><p>A phase change based (PCM) thermal management solution to keep a 50 kW PEM fuel cell stack warm during dormancy in a cold climate (-20 °C) was investigated through simulation and experiments. It was shown that a combination of PCM (salt hydrate or paraffin wax) and vacuum insulation materials was able to keep a fuel cell stack from freezing for about three days. This is a simple and potentially inexpensive solution, although development on issues such as weight, volume and encapsulation materials is needed </p><p>Two different vehicle platforms, fuel cell vehicles and fuel cell hybrid vehicles, were used to study the fuel consumption and the air, water and heat management of the fuel cell system under varying operating conditions, <i>e.g.</i> duty cycles and ambient conditions. For a compact vehicle, with a 50 kW fuel cell system, the fuel consumption was significantly reduced, ~ 50 %, compared to a gasoline-fuelled vehicle of similar size. A bus with 200 kW fuel cell system was studied and compared to a diesel bus of comparable size. The fuel consumption of the fuel cell bus displayed a reduction of 33-37 %. The performance of a fuel cell hybrid vehicle,<i> i.e.</i> a 50 kW fuel cell system and a 12 Ah power-assist battery pack in series configuration, was studied. The simulation results show that the vehicle fuel consumption increases with 10-19 % when the altitude increases from 0 to 3000 m. As expected, the air compressor with its load-following strategy was found to be the main parasitic power (~ 40 % of the fuel cell system net power output at the altitude of 3000 m). Ambient air temperature and relative humidity affect mostly the fuel cell system heat management but also its water balance. In designing the system, factors such as control strategy, duty cycles and ambient conditions need to taken into account.</p><p>An evaluation of the performance and maintenance of three fuel cell buses in operation in Stockholm in the demonstration project Clean Urban Transport for Europe (CUTE) was performed. The availability of the buses was high, over 85 % during the summer months and even higher availability during the fall of 2004. Cold climate-caused failures, totalling 9 % of all fuel cell propulsion system failures, did not involve the fuel cell stacks but the auxiliary system. The fuel consumption was however rather high at 7.5 L diesel equivalents/10km (per July 2004). This is thought to be, to some extent, due to the robust but not energy-optimized powertrain of the buses. Hybridization in future design may have beneficial effects on the fuel consumption. </p><p>Surveys towards hydrogen and fuel cell technology of more than 500 fuel cell bus passengers on route 66 and 23 fuel cell bus drivers in Stockholm were performed. The passengers were in general positive towards fuel cell buses and felt safe with the technology. Newspapers and bus stops were the main sources of information on the fuel cell bus project, but more information was wanted. Safety, punctuality and frequency were rated as the most important factors in the choice of public transportation means. The environment was also rated as an important factor. More than half of the bus passengers were nevertheless unwilling to pay a higher fee for introducing more fuel cell buses in Stockholm’s public transportation. The drivers were positive to the fuel cell bus project, stating that the fuel cell buses were better than diesel buses with respect to pollutant emissions from the exhausts, smell and general passenger comfort. Also, driving experience, acceleration and general comfort for the driver were reported to be better than or similar to those of a conventional bus.</p>

An assessment study of a novel approach is presented that combines discrete state-space Dynamic Programming and Pontryagin’s Maximum Principle for online optimal control of hybrid electric vehicles (HEV). In addition to electric energy storage and gear, kinetic energy and travel time are considered states in this paper. After presenting the corresponding model using a parallel HEV as an example, a benchmark method with Dynamic Programming is introduced which is used to show the solution quality of the novel approach. It is illustrated that the proposed method yields a close-to-optimal solution by solving the optimal control problem over one hundred thousand times faster than the benchmark method. Finally, a potential online usage is assessed by comparing solution quality and calculation time with regard to the quantization of the state space.

In this thesis, direct hydrogen Proton Exchange Membrane (PEM) fuel cell systems in vehicles are investigated through modelling, field tests and public acceptance surveys. A computer model of a 50 kW PEM fuel cell system was developed. The fuel cell system efficiency is approximately 50% between 10 and 45% of the rated power. The fuel cell auxiliary system, e.g. compressor and pumps, was shown to clearly affect the overall fuel cell system electrical efficiency. Two hydrogen on-board storage options, compressed and cryogenic hydrogen, were modelled for the above-mentioned system. Results show that the release of compressed gaseous hydrogen needs approximately 1 kW of heat, which can be managed internally with heat from the fuel cell stack. In the case of cryogenic hydrogen, the estimated heat demand of 13 kW requires an extra heat source. A phase change based (PCM) thermal management solution to keep a 50 kW PEM fuel cell stack warm during dormancy in a cold climate (-20 °C) was investigated through simulation and experiments. It was shown that a combination of PCM (salt hydrate or paraffin wax) and vacuum insulation materials was able to keep a fuel cell stack from freezing for about three days. This is a simple and potentially inexpensive solution, although development on issues such as weight, volume and encapsulation materials is needed Two different vehicle platforms, fuel cell vehicles and fuel cell hybrid vehicles, were used to study the fuel consumption and the air, water and heat management of the fuel cell system under varying operating conditions, e.g. duty cycles and ambient conditions. For a compact vehicle, with a 50 kW fuel cell system, the fuel consumption was significantly reduced, ~ 50 %, compared to a gasoline-fuelled vehicle of similar size. A bus with 200 kW fuel cell system was studied and compared to a diesel bus of comparable size. The fuel consumption of the fuel cell bus displayed a reduction of 33-37 %. The performance of a fuel cell hybrid vehicle, i.e. a 50 kW fuel cell system and a 12 Ah power-assist battery pack in series configuration, was studied. The simulation results show that the vehicle fuel consumption increases with 10-19 % when the altitude increases from 0 to 3000 m. As expected, the air compressor with its load-following strategy was found to be the main parasitic power (~ 40 % of the fuel cell system net power output at the altitude of 3000 m). Ambient air temperature and relative humidity affect mostly the fuel cell system heat management but also its water balance. In designing the system, factors such as control strategy, duty cycles and ambient conditions need to taken into account. An evaluation of the performance and maintenance of three fuel cell buses in operation in Stockholm in the demonstration project Clean Urban Transport for Europe (CUTE) was performed. The availability of the buses was high, over 85 % during the summer months and even higher availability during the fall of 2004. Cold climate-caused failures, totalling 9 % of all fuel cell propulsion system failures, did not involve the fuel cell stacks but the auxiliary system. The fuel consumption was however rather high at 7.5 L diesel equivalents/10km (per July 2004). This is thought to be, to some extent, due to the robust but not energy-optimized powertrain of the buses. Hybridization in future design may have beneficial effects on the fuel consumption. Surveys towards hydrogen and fuel cell technology of more than 500 fuel cell bus passengers on route 66 and 23 fuel cell bus drivers in Stockholm were performed. The passengers were in general positive towards fuel cell buses and felt safe with the technology. Newspapers and bus stops were the main sources of information on the fuel cell bus project, but more information was wanted. Safety, punctuality and frequency were rated as the most important factors in the choice of public transportation means. The environment was also rated as an important factor. More than half of the bus passengers were nevertheless unwilling to pay a higher fee for introducing more fuel cell buses in Stockholm’s public transportation. The drivers were positive to the fuel cell bus project, stating that the fuel cell buses were better than diesel buses with respect to pollutant emissions from the exhausts, smell and general passenger comfort. Also, driving experience, acceleration and general comfort for the driver were reported to be better than or similar to those of a conventional bus. / QC 20101020

Η θεματολογία της εργασίας αυτής περιλαμβάνει την υβριδική τεχνολογία στην αυτοκίνηση. Γίνεται μία εκτεταμένη ανάλυση των υβριδικών οχημάτων, αρχικά κάνοντας αναφορά στην ιστορία των υβριδικών και μη οχημάτων και έπειτα στα περιβαλλοντικά θεμάτα που τα έφεραν στο προσκήνιο. Η ανάλυση περιλαμβάνει επίσης την μελέτη των διαφόρων κατηγοριών υβριδικών οχημάτων, την εξέταση των κατασκευαστικών μερών τους και κλείνει με την παρουσίαση κάποιων χαρακτηριστικών οχημάτων που βγήκαν στην παραγωγή. Στη συνέχεια, η εργασία περνά στο πειραματικό της στάδιο, που περιλαμβάνει τη μελέτη και κατασκευή ενός ηλεκτροκινητήριου συστήματος για εφαρμογή σε πειραματικό όχημα. Το όχημα μετά τις επεμβάσεις θα είναι υβριδικό, κάνοντας χρήση δύο πηγών ενέργειας, ορυκτά καύσιμα και ηλεκτρισμό. Έγινε η προμήθεια του οχήματος και των απαραίτητων μερών του συστήματος δηλαδή ενός ασύγχρονου ηλεκτροκινητήρα και των μπαταριών, που είναι τύπου οξέος-μολύβδου. Ακολούθησαν μηχανολογικές μετατροπές στο αμάξωμα ώστε να δεχθεί το πρόσθετο σύστημα μετάδοσης κίνησης, οι οποίες και αναλύονται. Παράλληλα βρίσκονταν σε εξέλιξη οι μετατροπείς ισχύος που απαιτούνται στο σύστημα ηλεκτρικής κίνησης για να προσαρμόσουν τα ηλεκτρικά μεγέθη κατάλληλα ώστε να επιτρέψουν την ροή ισχύος από τις μπαταρίες προς τον κινητήρα, κατά την επιτάχυνση του οχήματος, και την επιστροφή ενέργειας στις μπαταρίες από τη μηχανή, που λειτουργεί ως γεννήτρια λαμβάνοντας ενέργεια από την κινητική του οχήματος. Οι απαιτούμενοι μετατροπείς είναι ένας αμφικατευθυντήριος μετατροπέας ανύψωσης – υποβιβασμού συνεχούς τάσης σε συνεχή και ένας μετατροπέας συνεχούς τάσης σε τριφασική εναλλασσόμενη, ή πιο απλά τριφασικός αντιστροφέας. Ο δεύτερος μετατροπέας πραγματοποιεί και τον έλεγχο της ροπής που παράγει σε κάθε στιγμή ο κινητήρας μέσω της μεθόδου του Άμεσου Έλεγχου Ροπής (DTC). Περιγράφονται οι μεθοδολογίες ελέγχου των τριφασικών ασύγχρονων κινητήρων και γίνεται λεπτομερής ανάλυση της χρησιμοποιούμενης μεθόδου. Στο τελευταίο τμήμα περιγράφονται οι πειραματικές μετρήσεις που διεξήχθησαν με το σύστημα που κατασκευάστηκε, στον εργαστηριακό πάγκο και επί του οχήματος της εφαρμογής. Τέλος, γίνεται ανάλυση των αποτελεσμάτων που προέκυψαν. / The subject of this work includes the use of hybrid technology in automotive. An extensive analysis of hybrid vehicles is carried out, referring to the history of hybrid and other vehicles and then to the environmental matters that brought hybrids to the fore. The analysis also includes the study of different types of hybrid vehicles, examining their components and ends with the presentation of some remarkable vehicles that have been produced. The work then passes into the experimental phase, involving the design and construction of an electric system to be applied in a conventional vehicle. The vehicle is meant to function as a hybrid, using two energy sources, fossil fuels and electricity. For the reason, a vehicle has been supplied along with the necessary parts of the system, which consist of an asynchronous electric motor and lead acid batteries. Mechanical modifications that were made to the chassis to accept the additional drivetrain are discussed in detail. The construction of the necessary power converters is carried out in parallel. Their purpose is to adjust the electrical values in order to allow the flow of power from the batteries to the engine during acceleration of the vehicle and return energy to the batteries from the electrical machine, which acts as generator powered from the vehicle’s wheels.. The required converters are: a bi-directional buck/boost DC to DC converter and a three-phase DC to AC converter, which is simply described as inverter. The second converter also performs the control of the torque produced at any time from the engine, using Direct Torque Control (DTC). Alternate methodologies are also described, while the used technique is fully analyzed. The final section describes the experimental procedures performed to the constructed systems. At first they are tested in the laboratory and afterwards they are applied on the vehicle. Finally, an analysis of the results is performed.

Electric and hybrid vehicles are particularly suited for use in urban areas since city transportation is mainly characterized by relatively short driving distances, low continuous power requirements, long idling times and high availability of regenerative braking energy. These characteristics, when carefully incorporated into the design process, create valuable opportunities for developing clean, efficient and cost effective urban vehicle propulsion systems. In the first part of the thesis, we present data collected in the city of Bangalore, India from a very commonly seen mode of transportation for hire in India and other emerging economies, namely a three-wheeled vehicle known as the “auto-rickshaw”. From a statistical analysis, it is shown that the typical range is 72.5 km with a mean speed of 12.5 km/h. More than 60% of the time the auto-rickshaw is stationary or has a speed of less than 5 km/h. From a model of the auto-rickshaw, it is shown from simulations that 4 kW DC motor and about 10 kWh of electrical energy is enough to meet 80% of typical requirement. Based on this finding, in this thesis, a novel parallel hybrid architecture is proposed where two 2 kW DC hub motors are directly mounted on the wheels and an internal combustion (IC) engine output is connected to the stator of the DC hub motors to provide additional power when required. To match load and speed, a continuously variable transmission (CVT) is placed in-between the IC engine and the DC hub motor. The proposed hybrid configuration adds speed to the wheel output unlike the normal power split configuration which adds torque. One of the main objective of this work is to study and compare the performance of the above novel speed-addition and compare with the typical torque-addition configuration. A MATLAB/Simulink model for both the configurations, with DC hub motor and a small IC engine, has been created and the fuel consumption has been calculated. It is shown that the proposed speed-addition concept gives better fuel efficiency for the standard modified Indian Driving Cycle. The models have also been compared for actual driving data and an optimal control strategy has been developed using dynamic programming. It is again shown that the proposed speed-addition concept results in better fuel economy. In the last part of the thesis, a low cost experimental test-bed consisting of an auto-rickshaw IC engine, a CVT and a 2 kW DC hub motor has been developed to validate the speed-addition concept and compare with the torque-addition configuration. The torque-speed curves of the IC engine, the DC motor and both of them together, in the speed and torque-addition configuration, have been obtained. It is shown that the speed-addition concept does indeed work and the obtained results are significantly different from the torque-addition configuration.

An assessment study of a novel approach is presented that combines discrete state-space Dynamic Programming and Pontryagin’s Maximum Principle for online optimal control of hybrid electric vehicles (HEV). In addition to electric energy storage and gear, kinetic energy and travel time are considered states in this paper. After presenting the corresponding model using a parallel HEV as an example, a benchmark method with Dynamic Programming is introduced which is used to show the solution quality of the novel approach. It is illustrated that the proposed method yields a close-to-optimal solution by solving the optimal control problem over one hundred thousand times faster than the benchmark method. Finally, a potential online usage is assessed by comparing solution quality and calculation time with regard to the quantization of the state space.