The core of any electric vehicle (EV) is the electric drive train, intended as the energy conversion chain from the energy tank (typically some kind of rechargeable battery) to the electric motor that converts the electrical energy into the mechanical energy needed for the vehicle motion. The need for on-board electrical energy storage is the factor that has so far prevented pure electric vehicles from conquering significant market share. In fact electrochemical batteries, which are currently the most suitable device for electrical energy storage, have serious limitations in terms of energy and/or power density, cost and safety. All those characteristics reflect in pure electric vehicles being outperformed by standard internal combustion engine (ICE) based vehicles in terms of driving range, time needed to refuel and purchase cost. Electric vehicles do have their distinctive advantages, being intrinsically much more efficient, operating at zero emissions at the pipe, and offering a higher degree of controllability that can potentially enhance driving safety. No wonder then, that electric energy storage technology has attracted considerable R&D investments, resulting in new traction battery packs that are getting closer and closer to the industrial targets. In this scenario of EV technology gaining momentum, power electronics engineers have to come up with newer solutions allowing for more efficient and more reliable utilization of the precious on-board energy that comes in a form that cannot be directly utilized by the motor. At present, most of the research in the area of power electronics for automotive is focused in volume and cost reduction techniques. The increase in power density is pursued by developing components that can be operated at higher temperature, thus relieving the requirements on cooling. In this thesis, the focus is on the development of alternative topologies for the power electronics converters that make use of some peculiarities of the energy storage components and of the electrical drive train in general, rather than being a mere component-level optimization of well established topologies. A novel converter topology is proposed for hybridization of the energy source with a supercapacitor-based power buffer being used to assist the main traction battery. From the functional point of view, the topology implements a bidirectional DC/DC converter. Making use of the fact that the battery terminal voltage is close to constant, an arrangement for the supercapacitors is devised allowing for bidirectional power flow by using power electronics devices of lower ratings than the ones needed in conventional DC/DC converters. At the same time, much smaller magnetic components are needed. Theoretical analysis of the operation of the proposed converter is given, allowing for optimized design. A full-scale experimental prototype rated at 30 kW, intended for use in a pure EV, has been built and tested. Results validate the theory and show that no particular impediment exist to the deployment of the concept in practical applications. Another concept introduced in the thesis is an architecture where the traction inverter is embedded in the energy storage device. The latter is constituted by several modules, as in the case of modern Li-ion battery systems, and each module is equipped with a local power electronics interface, making it functionally equivalent to a controllable voltage source. The result is a modular, distributed system that can be engineered to have very high reliability and also to exhibit self-healing properties. A prototype with a minimum number of modules has been built and tested. Results confirm the effectiveness of the system, and make it a good candidate for deployment in applications where reliability is the most important requirement.

This works begins by providing motivation for additional research and political interest in the use of passenger railway systems as a method of ‘green’ transportation. Additional motivation for the adoption of energy saving methods within new and existing railway systems is also provided. This motivation stems from the relatively small carbon dioxide emissions per passenger kilometer and large quantity of electrical energy used in association with passenger railway systems. In specific cases, both theoretical analyses and experimental implementations of energy storage in railway systems have shown a reduction in electrical energy use and/or vehicle performance gains. Current railway energy storage systems (ESS) commonly make use of battery or electric double layer capacitor (EDLC) cells. A review of select energy storage technologies and their application in railway systems is provided. For example, the developing Qatar Education City People Mover system makes use of energy dense batteries and power dense EDLCs to provide the range and power needed to operate without a conventional railway power source between stations, formally called catenary free operation. As an alternative to combining two distinct energy storage technologies, this work looks at experimentally characterizing the performance of commercially available lithium ion capacitors (LiCs); a relatively new energy storage cell that combines characteristics of batteries and EDLCs into one cell. The custom cell testing apparatus and lab safety systems used by this work, and others, is discussed. A series of five tests were performed on two EDLC cells and five LiC cells to evaluate their characteristics under various electrical load conditions at multiple temperatures. The general conclusion is that, in comparison to the EDLC cells tested, the LiC cells tested offer a superior energy density however, their power capabilities are relatively limited, especially in cold environments, due to larger equivalent series resistance values. The second topic explored in this work is the development of a MATLAB based DC powered passenger vehicle railway simulation tool. The simulation tool is connected to the experimental analysis of EDLC and LiC cells by comparing the volume and mass of an energy storage system needed for catenary free (no conventional DC power supply) operation between train stations using either energy storage technology. A backward facing modelling approach is used to quantify the drive cycle electrical power demands as a function of multiple vehicle parameters and driving parameters (eg. acceleration rate, travel distance and time). Additional modelling methods are provided as a resource to further develop the simulation tool to include multiple vehicles and their interactions with the DC power supply. Completion of the multi-vehicle simulation tool with energy storage systems remains a task for future work. / Thesis / Master of Applied Science (MASc)

An electrochemical double-layer capacitor (EDLC) is a potential buffer for current power and energy supply. In this work, activated carbon derived from fluid coke as a brand new electrode material was studied due to its high specific surface area (SSA) and large portion of mesopores. A suitable electrode material formula, current collector, and cell configuration were investigated to fabricate a testable system and ensure the reproducibility of measurements. Cyclic voltammetry (CV) and constant current charge/discharge (CD) techniques were used to characterize the performance of the electrode material, as well as to study its fundamental behaviour. A new procedure was established for quantifying the capacitance (Cc) of EDLC from CV which isolates the effect of internal resistance on the measured capacitance (CM). The specific capacitance of single electrode made of activated carbon (~1900 m2/g) with approximately 80% mesopores and macropores was able to reach 180 F/g at scan rate of 0.5mV/s.

An electrochemical double-layer capacitor (EDLC) is a potential buffer for current power and energy supply. In this work, activated carbon derived from fluid coke as a brand new electrode material was studied due to its high specific surface area (SSA) and large portion of mesopores. A suitable electrode material formula, current collector, and cell configuration were investigated to fabricate a testable system and ensure the reproducibility of measurements. Cyclic voltammetry (CV) and constant current charge/discharge (CD) techniques were used to characterize the performance of the electrode material, as well as to study its fundamental behaviour. A new procedure was established for quantifying the capacitance (Cc) of EDLC from CV which isolates the effect of internal resistance on the measured capacitance (CM). The specific capacitance of single electrode made of activated carbon (~1900 m2/g) with approximately 80% mesopores and macropores was able to reach 180 F/g at scan rate of 0.5mV/s.

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Surgical correction of scoliosis is a complicated mechanical process. Understanding the loads applied to the spine and providing immediate feedback to surgeons during scoliosis surgery will prevent overloading, improve surgical outcome and patient safety. Long-term development of residual forces in the spinal instrument after surgery with the continual curvature changes over time has been unknown. The goal of this research work was to develop a wireless implantable sensor platform to investigate the loads during and after surgery. This thesis describes research leading to the design of a sensor platform that uses both 403 MHz and 2.45 GHz for wireless communication, and reports the resolution and accuracy of the built-in temperature sensor, the A/D accuracy of the sensing platform, the power consumption at different operation modes, the range of the wireless communication and the discharge characteristics of a potential capacitive power module. / Biomedical Engineering

Hydrogen is considered one of the best alternatives to fossil-fuels for the transportation sector because hydrogen can be burnt cleanly and efficiently in a fuel cell to drive an electric motor. However, due to the low density of H2 at ambient conditions the conventional H2 storage technologies (cryogenic liquid and compressed gas) cannot achieve energy densities comparable to to gasoline and diesel. A second energy storage challenge onboard electric fuel cell vehicles is fuel cell power management at peak current loads, which requires an auxiliary power source like a battery or supercapacitor. The development of efficient onboard energy storage systems for H2 and auxiliary power is critical to realisation of a hydrogen economy. Mesoporous carbons were investigated as H2 storage materials in composites with magnesium hydride (MgH2),and as electrode materials for electrochemical double-later capacitors. The mesoporous carbons were prepared by two methods: (1) from porous silica and alumina templates, and (2) by chemical activation of a waste carbon source (waste coffee grounds). The experimental approach targeted reducing the cost of mesoporous carbon preparation by using a cheaper template, where the cost of alumina template was one-fifth the cost of the silica template (at the laboratory scale), or by using a waste material as a carbon source. The alumina template was found to be suitable to produce a mesoporous carbon with an average pore size of 4.8 nm. Chemical activation of coffee grounds with ZnCl2 produced activated carbons with BET surface areas up to 1280 m2/g. Mesopore volume increased with ZnCl2 impregnation ratio, with mesopore size distributions in the range 2 - 20 nm. The theoretical H2 capacity of MgH2 is 7.6 % but MgH2 application in fuel cell vehicles is limited by slow hydrogenation kinetics and high temperatures (> 573 K) for H2 release. Magnesium was impregnated on activated carbon fibres (ACF) and mesoporous carbon (prepared from silica and alumina templates) to improve H2 storage kinetics and thermodynamics by reducing the magnesium hydride particle size. Thermal gravimetric analysis (TGA) and temperature programmed desorption (TPD) studies showed that thermal decomposition of MgCl2 supported on ACF at 1173 K in N2 and H2 can produce a Mg-ACF composite. At 573 K and 2 MPa H2 pressure a Mg-ACF composite, containing 11.2 %wt Mg, showed improved H2 adsorption kinetics compared to bulk Mg powder, but the total capacity of the Mg-ACF composite was only 0.4 % wt H2. To achieve a target of 6 %wt for onboard H2 storage higher Mg loadings are required. Attempts to impregnate Mg in mesoporous carbon via the MgCl2 thermal decomposition process highlighted the difficulties of avoiding MgO formation, and show that MgH2 loaded carbon is unlikely to be a practical high density onboard H2 storage technology. Activated carbons from waste coffee grounds (CGCs) were used as electrode materials in electrochemical double-layer capacitors. The specific capacitance of CGCs was as high as 368 F/g in 1 mol/L H2SO4, with good capacitance retention at fast charge rates and stable cycling performance. The good electrochemical performance of CGCs is attributed to a porous structure featuring both micropores 0.5 - 1.0 nm wide, which are effective for double-layer formation, and small mesopores, which facilitate electrolyte transport at fast charge rates. The capacitance of CGCs is enhanced by pseudo-Faradaic reactions involving nitrogen and oxygen functional groups. At fast charge-discharge rates the CGCs had higher energy density and better stability than a commercial benchmark activated carbon (Maxsorb). The ZnCl2 activation process can be optimised to develop mesopores for improved capacitance at fast charge rates and capacitance in organic electrolytes. In 1 mol/L tetra ethyl ammonium tetrafluoroborate (TEABF4) / acetonitrile the CGC with the most mesopores, which was prepared with a ZnCl2 to coffee ratio of 5:1, has the highest capacitance at high power density. CGCs with greater mesopore content retained higher specific capacitance at fast charge-discharge rates as the mesopores acts as channels or reservoirs for electrolyte transport. An improved model for evaluation of contributions to capacitance from micropore surfaces and mesopore surfaces is proposed. From this model the double-layer capacitance of mesopores surface area was found to be about 14 μF/cm2 and did not change considerably with increasing current load. The contribution of micropores to capacitance is dependent on the accessibility of ions to the micropores, and this accessibility is proportional to the mesopore surface area. An exponential function was found to describe the contribution of mesopores and micropore surfaces to capacitance. The effective double-layer capacitance of the micropore surface area drops at fast charge-discharge rates as a result of restricted ion transport, and this result highlights the importance of mesopores to retain energy density for high power supercapacitor applications.

Energy storage devices are generally evaluated on two main requirements; power and energy. In supercapacitors these two performance criteria are altered by the capacitance, resistance and voltage. (For complete abstract open document)

In this research we have investigated electrochemical and impedance characteristics of liquid phase exfoliated graphene electrodes. The exfoliated graphene electrodes were characterized in Electrochemical Double Layer Capacitors (EDLCs) geometry. Liquid phase exfoliation was performed on bulk graphite powder in order to produces few layer graphene flakes in large quantities. The exfoliation processes produced few layer graphene based materials with increased specific surface area and were found to have suitable electrochemical charge storage capacities. Electrochemical evaluation and performance of exfoliated graphene electrodes were tested with Cyclic Voltammetry, constant current charging discharging and Electrochemical Impedance Spectroscopy (EIS) at ambient conditions. We have used several electrolytes in order to evaluate the effect of electrolyte in charge storage capacities. Specific capacitance value of ~ 47F/g and ~ 262F/g was measured for aqueous and ionic electrolytes respectively. These values are at least an order of magnitude higher than those obtained by using EDLC's electrodes fabricated with the bulk graphite powder. In addition these EDLC electrodes give consistently good performance over a wide range of scan rates and voltage windows. These encouraging results illustrate the exciting potential for high performance electrical energy storage devices based on liquid phase exfoliated graphene electrodes.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21125号 / 工博第4489号 / 新制||工||1698(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 杉野目 道紀, 教授 吉田 潤一, 教授 松田 建児 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM