Indiana University-Purdue University Indianapolis (IUPUI) / This research introduces a new design of a converter modified from SEPIC converter (Single end primary inductive converter), capable of generating desired voltage levels and polarities. The new switching converter topology allows for boost and buck of the input voltage theoretically achieving infinite positive and negative voltage levels. The proposed topology utilizes single high frequency switch to perform the power conversion which simplifies the design of the gate driver, but meanwhile, it still retains the ability to provide a wide range of output voltage. Mathematical modeling of the converter and computer simulations are validated by experimental data. To verify its performance a prototype was designed and built. It is experimentally proven that the circuit can generate a desired voltage in the range of voltages up to ±170 V, delivering 480 Watts of power to a resistive load.

Outdoor insulators are one of the most important parts of a power system. The reliability of a power system depends also on the reliability of the insulators. The main functions of an insulator used for outdoor applications are to give the necessary insulation, provide the necessary mechanical support to the transmission line conductor and also to resist the various environmental stresses like pollution, ultra violet rays etc. Traditionally porcelain and glass insulators have been used for outdoor insulator applications. They are good insulators under normal conditions and the cap and pin arrangement allows them to take up the mechanical load of the line. But owing to their large weight and brittle nature they are susceptible to vandalism and also they have increased cost of installation and commissioning. But the main problem of porcelain and glass insulators is its performance under polluted environmental condition. Under wet and polluted conditions, the porcelain insulators allow the formation of a conducting layer on the surface which results in setting up of leakage current, dry band arcing and power loss. This problem is further augmented under dc voltages where the stress is unidirectional and the contaminant deposition is higher as compared to ac. Polymeric insulators are a good alternative for porcelain and ceramic insulators for use especially under dc voltages because of their good pollution performance. The property of surface hydrophobicity resists the setting up of leakage currents and hence polymeric insulators help in reducing power loss. They are also light in weight and vandalism resistant and hence easier to install. But being polymeric, they form conductive tracks and erode when exposed to high temperatures which occur at the surface during dry band arcs and when exposed to corona discharges. The surface hydrophobicity is also temporarily lost when exposed to different electrical stresses. Silicone rubber is the most popular among the various choices of polymers for outdoor insulator applications. They have good surface hydrophobicity and tracking performance. But polymers in their pure form cannot be used as insulators because of their poor mechanical strength. Adding inorganic fillers into the polymer matrix not only improves its mechanical properties but also its erosion resistance. Micron sized Alumina Trihydrate (ATH) is used traditionally to improve the tracking and erosion resistance of polymeric insulators. A very high loading (up to 60%) is used. Adding such a high filler loading to the base polymer hampers its flexibility and the material processing. With the advent of nanotechnology, nano fillers have come into vogue. Studies conducted on nano filled polymers showed exciting results. A small amount of nano fillers in the polymer matrix showed significant improvement in the mechanical strength without hampering its flexibility. The electrical properties like tracking and erosion also improved with filler loading. Hence the use of nano filled silicone rubber is a good alternative for use as a high voltage insulator especially under dc voltages. Reports suggest that adding nano fillers into the silicone rubber matrix improves the tracking and erosion resistance and the corona degradation as compared to the unfilled samples under ac voltages. The literature on the dc performance of silicone rubber nano composites is scarce. So the present study aims to evaluate the performance of silicone rubber nano composites for tracking and erosion resistance and corona degradation under dc voltages. The tracking and erosion resistance under dc voltages was measured using the Inclined Plane Tracking and Erosion Resistance set up as per ASTM D2303 which was modified for dc voltage studies. The performance of nano Alumina and nano Silica fillers were evaluated under negative dc and the performance was compared with micron sized Alumina Trihydrate filled samples. The effect of filler loading was also studied. It was seen that the performance of the silicone rubber improved with filler loading. A small loading percentage of nano fillers were enough to give performance similar to silicone rubber filled with micron sized ATH filler. The silicone rubber performed better under negative dc as compared to ac and positive dc. The positive dc tests showed a migration of ions from the electrodes onto the sample surface. The increased surface conductivity resulted in very heavy erosion in the case of positive dc tested samples. The corona aging studies were also conducted on silicone rubber nano composites. Nano silica was used as filler in this case. Different filler loadings were employed to understand the effect of filler loading. The corona was generated using a needle plane electrode and samples were exposed to both positive and negative dc corona. The samples were exposed to corona for different time intervals – 25 and 50 hours to study the effect of exposure time. The hydrophobicity, crack width and surface roughness were measured after the tests. Adding nano fillers into the polymer matrix improved the corona performance. With filler loading, the performance improved. The samples exposed to positive dc corona performed better than those under negative dc corona. The loss of hydrophobicity, surface cracks and the surface roughness was less in the case of positive dc corona tested samples. With exposure time, the performance of silicone rubber became poorer for positive dc corona tested samples. For the negative dc corona tested samples, the performance seemed to improve with exposure time. The tracking and erosion resistance and the corona aging studies conducted showed that the performance of silicone rubber is improved by adding nano fillers into the polymer matrix. A small amount of nano filler loading was enough to perform similar to a heavily loaded micron filled sample. Hence nano fillers can be used as a good functional material to improve the performance of silicone rubber insulators especially under wet and polluted conditions.

Thesis submitted in fulfillment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2013 / The development of power electronics did remove most of technical limitations that high voltage direct current (HVDC) used to have. HVDC, now, is mostly used for the transmission of bulk power over long distances and for the interconnection of asynchronous grid. Along with the development of the HVDC, the growth of power demand also increased beyond the utilities capacities. Besides the on-going increasing of power demand, the reforms in electricity market have led to the liberalization and the incorporation of Independent power providers in power system operation. Regulations and rules have been established by regulating authority for grid integration of Independent power providers. With the expected increase of penetration level of those new independent power providers, result of economic reason and actual green energy trend, best method of integration of those new power plants are required. In this research HVDC technology, namely VSC-HVDC is used as interface for connecting independent power providers units to the grid. VSC-HVDC has various advantages such as short-circuit contribution and independent control of active and reactive power. VSC-HVDC advantages are used for a safe integration of IPPs and make them participate to grid stabilization. MATLAB/Simulink simulations of different grid connected, through VSC-HVDC system, IPPs technologies models are performed. For each IPP technology model, system model performances are studied and dynamics responses during the disturbance are analyzed in MATLAB/ Simulink program. The simulation results show that the model satisfy the standard imposed by the regulating authority in terms of power quality and grid support. Also the results show the effect of the VSC-HVDC in preventing faults propagation from grid to integrated IPPs units.

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High voltage (EHV and UHV) transmission facilitates transfer of large amount of power over long distances. However, due to the inherent geometry, the line and substation hardware of EHV and UHV class generate high electric fields, which results in local ionisation of air called corona discharges. Apart from producing audible noise in the form of frying or hissing sound, corona produces significant electromagnetic interferences in the radio range. The limit for this corona generated Radio Interference (RI) has been stipulated by international standards, which are strictly to be followed. In line and substation hardware, corona control rings are generally employed to limit or avoid corona. Standard dimensions of corona rings are not available for EHV and UHV class. In most of the cases, their design is based on either a trial and error method or based on empirical extrapolation. Only in certain specific cases, the dimensioning of the rings is carried out using electric field calculations. In any of these approaches, the unavoidable surface abrasions, which can lead to corona, are not considered. There are also efforts to account for nominal surface irregularity by using a surface roughness factor, which is highly heuristic. In order to address this practically relevant problem, the present work was taken up. The intended exercise requires accurate field computation and a suitable criterion for checking corona onset. For the first part, the Surface Charge Simulation Method is adopted with newly proposed sub-modelling technique. The surface of the toroid is discretised into curvilinear patches with linear approximation for the surface charge density. Owing to its high accuracy, Galerkin’s method of moments formulation is employed. The problem of singularity encountered in the numerical approach is handled using a method based on Duffy’s transformation. The developed codes have also been validated with standard geometries. After a survey of relevant literature the ‘Critical Avalanche Criteria’ is chosen for its simplicity and applicability to the problem. Through a detailed simulation, the effect of avalanche space charge in reducing the corona onset voltage is found to be around 1.5% and hence it is not considered further. For utilities not interested in a detailed calculation procedure for dimensioning of corona rings, design curves are developed for circular corona rings of both 400 kV and 765 kV class with surface roughness factor in the range 0.8 – 1. In the second part of the work, a methodology for dimensioning is developed wherein the inevitable surface abrasion in the form of minute protrusions can be accounted. It is first shown that even though considerable field intensification occurs at the protrusions, such localised modification need not lead to corona. It is shown that by varying the minor radius of the corona ring, it is possible to get a design where the prescribed surface abrasion does not lead to corona onset. In summary, the present work has successfully developed a reliable methodology for the design of corona rings with prescribed surface abrasions. It involved development of an efficient field computation technique for handling minute surface protrusions and use of appropriate criteria for assessing corona inception. It has also provided design curves for EHV and UHV class corona rings with surface roughness factor specified in the range 0.8 – 1.0.

Indiana University-Purdue University Indianapolis (IUPUI) / Rechargeable lithium ion batteries are widely used in portable consumer electronics such as cellphones, laptops, etc. These batteries are capable to provide high energy density with no memory effect and they have small self-discharge when they are not in use, which increases their potential for future electric vehicles. Investigators are attempting to improve the performance of these cells by focusing on the energy density, cost, safety, and durability. The energy density improves with high operation voltage and high capacity. Before any further development of high voltage materials, safe electrolytes with high ionic conductivity, wide electrochemical window, and high stability with both electrodes need to be developed. In this thesis a new strategy was investigated to develop electrolytes that can contribute to the further development of battery technology. The first study is focused on preparing a hybrid electrolyte, the combination of inorganic solid and organic liquid, for lithium based rechargeable batteries to illustrate the effect of electrode/electrolyte interfacing on electrochemical performance. This system behaves as a self-safety device at higher temperatures and provides better performance in comparison with the solid electrolyte cell, and it is also competitive with the pure liquid electrolyte cell. Then a multilayer electrolyte cell (MEC) was designed and developed as a new tool for investigating electrode/electrolyte interfacial reactions in a battery system. The MEC consists of two liquid electrolytes (L.E.) separated by a solid electrolyte (S.E.) which prevents electrolyte crossover while selectively transporting Li+ ions. The MEC successfully reproduced the performance of LiFePO4 comparable with that obtained from coin cells. In addition, the origin of capacity fading in LiNi0.5Mn1.5O4full-cell (with graphite negative electrode) was studied using the MEC. The performance of LiNi0.5Mn1.5O4 MEC full-cell was superior to that of coin full-cell by eliminating the Mn dissolution problem on graphite negative electrode as evidenced by transmission electron microscopy (TEM) analysis. The MEC can be a strong tool for identifying the electrochemical performances of future high voltage positive electrode materials and their electrode/electrolyte interfacial reactions. Finally, by employing the multilayer electrolyte concept, a new application will be introduced to recycle the lithium. This study demonstrates the feasibility of using water and the contents of waste Li-ion batteries for the electrodes in a Li-liquid battery system. Li metal was collected electrochemically from a waste Li-ion battery containing Li-ion source materials from the battery’s anode, cathode, and electrolyte, thereby recycling the Li contained in the waste battery at the room temperature.

Cette thèse porte sur l'étude de micro-plasmas froids à la pression atmosphérique générés à partir de différents réacteurs des configurations basées sur le principe des Décharges à Barrière Diélectrique (DBD) et alimentés par des générateurs de tension impulsionnelle et sinusoïdale. Les plasmas sont formés dans des gaz nobles tels que l'hélium et l'argon (gaz vecteurs), et également dans des mélanges réalisés avec des gaz moléculaires tels que l'azote et l'oxygène afin de produire des Espèces Réactives de l’Azote et de l’Oxygène (ERA, ERO). La (ré)activité chimique du plasma est ainsi supposée être accrue, permettant le traitement de matériaux inertes ou vivants pour diverses applications (fonctionnalisation de surfaces, inactivation de cellules, régénération de tissus vivants, etc.). La caractérisation des plasmas étudiés est réalisée en enregistrant les aspects électriques et optiques en fonction des paramètres élémentaires, comme l’amplitude et la fréquence de la tension, le débit du gaz, la configuration des électrodes, et le rapport cyclique dans le cas du régime pulsé. Ainsi, la (ré)activité chimique des plasmas est évaluée tandis que au même temps les mécanismes de la génération des plasmas et les façons de l’optimisation de la chimie sont dévoilées. Finalement, nous examinons l'efficacité du plasma dans le domaine biomédical en traitant divers systèmes biologiques (bactéries, liposomes, cellules) sans effets thermiques. / The present PhD thesis is devoted to the study of atmospheric pressure cold micro-plasmas produced in different Dielectric Barrier Discharge (DBD) reactors which are driven by pulsed or sinusoidal high voltages. Noble gases such as helium and argon are used as carrier gases, whereas admixtures with nitrogen and oxygen are studied as well. The formation of Reactive Nitrogen and Oxygen Species (RNS, ROS) is thus achieved, and the possibility of improving the chemical (re)activity of the plasmas is demonstrated. This is of interest in the treatment of inert or living materials (e.g. surface functionalization, cell inactivation, living tissue regeneration, etc.). Plasmas are characterized by recording electrical and optical features as a function of principal operational parameters, including voltage amplitude and frequency, gas flow rate, electrode configuration, and voltage duty cycle in the case of pulsed waveform. The physico-chemical (re)activity of the plasmas is thus evaluated, while at the same time mechanisms on the plasma generation and paths for chemistry optimization are unveiled. Finally, the efficiency of the plasma in relation to biomedical applications is tested by treating different biological systems (bacteria, liposomes, cells) while preventing any thermal effect.

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