Integrated magnetic components for high-power high-current dc-dc converters

This thesis is focused on the design and development of an integrated magnetic (IM) structure for use in high-power high-current power converters employed in renewable energy applications. These applications require low-cost, high efficiency and high-power density magnetic components and the use of IM structures can help achieve this goal. A novel CCTT-core split-winding integrated magnetic (CCTT IM) is presented in this thesis. This IM is optimized for use in high-power dc-dc converters. The CCTT IM design is an evolution of the traditional EE-core integrated magnetic (EE IM). The CCTT IM structure uses a split-winding configuration allowing for the reduction of external leakage inductance, which is a problem for many traditional IM designs, such as the EE IM. Magnetic poles are incorporated to help shape and contain the leakage flux within the core window. These magnetic poles have the added benefit of minimizing the winding power loss due to the airgap fringing flux as they shape the fringing flux away from the split-windings. A CCTT IM reluctance model is developed which uses fringing equations to accurately predict the most probable regions of fringing flux around the pole and winding sections of the device. This helps in the development of a more accurate model as it predicts the dc and ac inductance of the component. A CCTT IM design algorithm is developed which relies heavily on the reluctance model of the CCTT IM. The design algorithm is implemented using the mathematical software tool Mathematica. This algorithm is modular in structure and allows for the quick and easy design and prototyping of the CCTT IM. The algorithm allows for the investigation of the CCTT IM boxed volume with the variation of input current ripple, for different power ranges, magnetic materials and frequencies. A high-power 72 kW CCTT IM prototype is designed and developed for use in an automotive fuelcell-based drivetrain. The CCTT IM design algorithm is initially used to design the component while 3D and 2D finite element analysis (FEA) software is used to optimize the design. Low-cost and low-power loss ferrite 3C92 is used for its construction, and when combined with a low number of turns results in a very efficient design. A paper analysis is undertaken which compares the performance of the high-power CCTT IM design with that of two discrete inductors used in a two-phase (2L) interleaved converter. The 2L option consists of two discrete inductors constructed from high dc-bias material. Both topologies are designed for the same worst-case phase current ripple conditions and this ensures a like-for-like comparison. The comparison indicates that the total magnetic component boxed volume of both converters is similar while the CCTT IM has significantly lower power loss. Experimental results for the 72 kW, (155 V dc, 465 A dc input, 420 V dc output) prototype validate the CCTT IM concept where the component is shown to be 99.7 % efficient. The high-power experimental testing was conducted at General Motors advanced technology center in Torrence, Los Angeles. Calorific testing was used to determine the power loss in the CCTT IM component. Experimental 3.8 kW results and a 3.8 kW prototype compare and contrast the ferrite CCTT IM and high dc-bias 2L concepts over the typical operating range of a fuelcell under like-for-like conditions. The CCTT IM is shown to perform better than the 2L option over the entire power range. An 8 kW ferrite CCTT IM prototype is developed for use in photovoltaic (PV) applications. The CCTT IM is used in a boost pre-regulator as part of the PV power stage. The CCTT IM is compared with an industry standard 2L converter consisting of two discrete ferrite toroidal inductors. The magnetic components are compared for the same worst-case phase current ripple and the experimental testing is conducted over the operation of a PV panel. The prototype CCTT IM allows for a 50 % reduction in total boxed volume and mass in comparison to the baseline 2L option, while showing increased efficiency.

High speed nonlinear optical components for next-generation optical communications

Electronic signal processing systems currently employed at core internet routers require huge amounts of power to operate and they may be unable to continue to satisfy consumer demand for more bandwidth without an inordinate increase in cost, size and/or energy consumption. Optical signal processing techniques may be deployed in next-generation optical networks for simple tasks such as wavelength conversion, demultiplexing and format conversion at high speed (≥100Gb.s-1) to alleviate the pressure on existing core router infrastructure. To implement optical signal processing functionalities, it is necessary to exploit the nonlinear optical properties of suitable materials such as III-V semiconductor compounds, silicon, periodically-poled lithium niobate (PPLN), highly nonlinear fibre (HNLF) or chalcogenide glasses. However, nonlinear optical (NLO) components such as semiconductor optical amplifiers (SOAs), electroabsorption modulators (EAMs) and silicon nanowires are the most promising candidates as all-optical switching elements vis-à-vis ease of integration, device footprint and energy consumption. This PhD thesis presents the amplitude and phase dynamics in a range of device configurations containing SOAs, EAMs and/or silicon nanowires to support the design of all optical switching elements for deployment in next-generation optical networks. Time-resolved pump-probe spectroscopy using pulses with a pulse width of 3ps from mode-locked laser sources was utilized to accurately measure the carrier dynamics in the device(s) under test. The research work into four main topics: (a) a long SOA, (b) the concatenated SOA-EAMSOA (CSES) configuration, (c) silicon nanowires embedded in SU8 polymer and (d) a custom epitaxy design EAM with fast carrier sweepout dynamics. The principal aim was to identify the optimum operation conditions for each of these NLO device configurations to enhance their switching capability and to assess their potential for various optical signal processing functionalities. All of the NLO device configurations investigated in this thesis are compact and suitable for monolithic and/or hybrid integration.

Sectoral impacts on the diversity of carabid beetles (Coleoptera: Carabidae) and their associated ecosystem service of biocontrol

This thesis aimed to provide an understanding of how human-induced changes in the economic sectors of agriculture and transport affect carabid diversity, potential carabidmediated biocontrol and predator-pest interactions. The research involved both observational and manipulative laboratory and field-based studies. Observational research consisted of two large-scale investigations of (1) the impact of Miscanthus and oilseed rape production (n=45) and (2) the impact of horticultural and ecological based landscaping of roadside verges (n=64). This research is the first record of carabid diversity, potential biocontrol and community assemblage with respect to bioenergy crop production and roadside landscaping in an Irish context and it is also an important addition to the limited knowledge of carabid populations in these ecosystems internationally. Manipulative work involved the examination of the role predator identity, diversity and biomass play in the suppression of pollen beetle larvae (an economically damaging insect pest of oilseed rape in Europe), using a novel experimental design called ‘simplex’. To complement this research, an additional field study on the impact of low and high oilseed rape pesticide management on carabid species richness and abundance, and crop yield, was also conducted. This research is a great contribution to the existing understanding of what constitutes the important components of predator biodiversity and expands the knowledge of the usefulness of carabid predators in the context of pollen beetle larvae control. In particular, the work shows that the abundance or biomass of beetles has an effect that is far larger than the effect of diversity on the capacity of beetles to consume prey. In turn, the field study showed that pesticide applications had little impact on yield, or carabid richness, but that carabid abundance/biomass declined drastically. The work provides compelling evidence that management practices erode the useful components of biodiversity that are essential for the delivery of biocontrol services.

Investigation of lantibiotic regulation, immunity and synergy

Due to the increasing incidence of antibiotic resistant strains, the use of novel antimicrobials, such as bacteriocins, has become an ever more likely prospect. Lacticin 3147 (of which there are two components, Ltnα and Ltnβ) and nisin belong to the subgroup of bacteriocins called the lantibiotics, which has attracted much attention in recent years. The lantibiotics are antimicrobial peptides that contain unusual amino acids resulting from a series of enzyme-mediated post translational modifications. Given that there have been relatively few examples of lantibiotic-specific resistance; these antimicrobials appear to represent valid alternatives to classical antibiotics. However, the fact that lantibiotics are naturally only produced in small amounts often hinders their commercialisation. In order to overcome this bottleneck, several approaches can be employed. For example, we can create a situation that reduces the quantity of a lantibiotic required to inhibit a target by combining it with other antimicrobials. Here, following an initial screen involving lacticin 3147 and several classical antibiotics, it was observed between lacticin 3147 and the commercial antibiotics polymyxin B/E function synergistically. This reduced the amounts of the individual antimicrobials required for kill and broadened the spectrum of inhibition of both agents. Upon combination with polymyxins, lacticin 3147, which has been associated with Gram positive targets only, actively targeted Gram negative species such as Escherichia coli and Cronobacter sp. An alternative means of addressing problems associated with lantibiotic yield is to better understand how production is regulated, and ultimately use this information to enhance peptide levels. With this in mind the regulation of lacticin 3147 production from the promoter Pbac was investigated using a green fluorescent protein (GFP) expression reporter system. This revealed that elements within both of the divergent operons of the lacticin 3147 gene cluster are involved in Pbac regulation. That is, LtnR, already established as a negative regulator of itself and the lacticin 3147 associated immunity genes, also acts as an activator of Pbac transcription. In contrast, an enhanced level of expression is observed in the absence of the lacticin 3147 structural genes, ltnA1 and ltnA2, indicating that these genes/gene products are involved in Pbac repression. In fact, through complementation of the ltnA2 gene, it was revealed that this regulation is more likely to be dependent on the presence of the gene transcript rather that the corresponding prepropeptide or modified Ltnβ. It may be that if lacticin 3147 production is successfully enhanced, the ability of the producing cell to protect itself may become an issue. To prepare for such a possibility a bioengineered derivative of the lacticin 3147 immunity protein LtnI (LtnI I81V) which provides enhanced protection was discovered through an in depth investigation involving the site and saturation mutagenesis of this protein. In addition, the creation of truncated forms of LtnI allowed the identification of important and essential regions of this immunity protein. Finally, as mentioned, self-immunity is essential to prevent self-killing. However the discovery of nisin U immunity and regulatory gene homologues (spiFEGRR’K) within the pathogenic strain S. infantarius subsp. infantarius is a cause for concern as it represents an example of immune mimicry, a form of lantibiotic-specific resistance. The ability of spiFEG to confer protection was apparent when they successfully provided protection to nisin A, F, Z, Q and U when expressed heterologously in the nisin sensitive L. lactis HP host. As a consequence of the studies presented in this thesis, it is likely that strategies will emerge that will facilitate the production of greater levels of lacticin 3147 production and lead to enhanced immunity in lactococcal backgrounds. Alternatively the need for enhanced production could be avoided through the use of antimicrobial combinations. In addition, providing awareness of the threats of the emergence of resistance through immune mimicry can allow researchers to develop strategies to prevent this phenomenon from leading to the dissemination of lantibiotic resistance.

Design, fabrication and characterisation of components for microfluidic enzymatic biofuel cells

The concept of a biofuel cell takes inspiration from the natural capability of biological systems to catalyse the conversion of organic matter with a subsequent release of electrical energy. Enzymatic biofuel cells are intended to mimic the processes occurring in nature in a more controlled and efficient manner. Traditional fuel cells rely on the use of toxic catalysts and are often not easily miniaturizable making them unsuitable as implantable power sources. Biofuel cells however use highly selective protein catalysts and renewable fuels. As energy consumption becomes a global issue, they emerge as important tools for energy generation. The microfluidic platforms developed are intended to maximize the amount of electrical energy extracted from renewable fuels which are naturally abundant in the environment and in biological fluids. Combining microfabrication processes, chemical modification and biological surface patterning these devices are promising candidates for micro-power sources for future life science and electronic applications. This thesis considered four main aspects of a biofuel cell research. Firstly, concept of a miniature compartmentalized enzymatic biofuel cell utilizing simple fuels and operating in static conditions is verified and proves the feasibility of enzyme catalysis in energy conversion processes. Secondly, electrode and microfluidic channel study was performed through theoretical investigations of the flow and catalytic reactions which also improved understanding of the enzyme kinetics in the cell. Next, microfluidic devices were fabricated from cost-effective and disposable polymer materials, using the state-of-the-art micro-processing technologies. Integration of the individual components is difficult and multiple techniques to overcome these problems have been investigated. Electrochemical characterization of gold electrodes modified with Nanoporous Gold Structures is also performed. Finally, two strategies for enzyme patterning and encapsulation are discussed. Several protein catalysts have been effectively immobilized on the surface of commercial and microfabricated electrodes by electrochemically assisted deposition in sol-gel and poly-(o-phenylenediamine) polymer matrices and characterised with confirmed catalytic activity.

Profiling phytochemical and nutritional components of potato

Potatoes (Solanum Tuberosum L.) contain secondary metabolites that may have an impact on human health. The aim of this study was to assess the levels of some of these compounds in a wide range of varieties, including rare, heritage and commercial cultivars. Vitamin C, total carotenoids, phenolics, flavonoids, antioxidant activity and glycoalkaloids were determined, using spectroscopy and chromatography, in the skin and flesh of tubers grown in field trials. Transcript levels of key synthetic enzymes were assessed by qPCR. Accumulation of selected metabolites was higher in the skin than in the flesh of tubers, except ascorbate, which was undetected in the skin. Differences were on average 2.5 to 3-fold for carotenoids, 6-fold for phenolics, 15 to 16-fold for flavonoids, 21-fold for glycoalkaloids and 9 to 10-fold for antioxidant activity. Higher contents of carotenoids were associated with yellow skin or flesh, and higher values of phenolics, flavonoids and antioxidant activity with blue flesh. Variety ‘Burren’ had maxima values of carotenoids in skin and flesh, variety ‘Nicola’ of ascorbate, variety ‘Congo’ of phenolics, flavonoids and antioxidant activity in both tissues, except antioxidant activity in the skin, which was higher in ‘Edzell Blue’. Varieties ‘May Queen’ and ‘International Kidney’ had highest glycoalkaloid content in skin and flesh respectively. The effect of the environment was diverse: year of cultivation was significant for all metabolites, but site of cultivation was not for carotenoids and glycoalkaloids. Levels of expression of phenylalanine ammonia-lyase and chalcone synthase were higher in varieties accumulating high contents of phenolic compounds. However, levels of expression of phytoene synthase and L-galactono-1,4-lactone dehydrogenase were not different between varieties showing contrasting levels of carotenoids and ascorbate respectively. This work will help identify varieties that could be marketed as healthier and the most suitable varieties for extraction of high-value metabolites such as glycoalkaloids.