In recent years, electrical double layer capacitor (EDLCs) has become one of the most popular energy storage devices. This can be attributed to its high capacity, long life cycle and fast charge/discharge rates. However, it has some drawbacks – mainly it stores less amount of energy than batteries. Hence, there is a need to optimize the EDLC to increase its capacity and decrease its equivalent series resistance (ESR), resulting in a supercapacitor that is able to charge quickly and will hold a large amount of energy for a long time. This thesis presents a design, build and setup process of a supercapacitor pilot plant in the University of Nottingham Malaysia Campus for manufacturing and optimization of EDLCs. Two packages were considered, cylindrical and coin type packages. In addition, the design of a manufacturing process flow, with details on steps for fabrication, which will meet specific standards (BS EN 62391-1:2006, BS EN 62391-2-1: 2006, BS EN 62391-2-1: 2006 and DOD-C-29501/3 NOT 1) for quality and throughput for both the packaging types is discussed. Following this, significant factors of the fabrication process were identified and optimized by adopting the Taguchi design of experiment (DOE) methodology. Results of the optimization process show that the most significant factors that affect the EDLC capacitance are PVDF % (polyvinylidene diflouride) and mixing time; the optimum values are determined to be 5% and 3 hours respectively. In the case of ESR optimization, the most significant factors are PVDF % and carbon black %. The optimum values are 5% for both. Using these optimized values, a final prototype EDLC was fabricated. The capacitance value obtained for the cell was 54.70mF. The final EDLC prototypes were tested according to the international standards (ISO) and compared with the supercapacitors available in the market. Results indicated that the electrochemical performance of the prototypes has a good resemblance to the performance of the supercapacitors available in the market. A selected prototype samples were sent for benchmark testing to companies in mobile applications in Korea and the Netherlands to confirm that the prototypes meet the required standards. Finally the research work sets the basis for integrating genetic algorithms with the Taguchi technique for future research in improving the optimization process for robust EDLC fabrication.

This thesis describes experimental and theoretical research into triple barrier resonant tunnelling structures which are attractive as potential high frequency oscillators in the terahertz frequency range. A lack of practical and coherent radiation emitters in this frequency range has resulted in it being named the \terahertz gap". However resonant tunnelling structures are seen as potential sources for practical solid state emitters which operate in this frequency range at room temperature. A series of symmetric and asymmetric GaAs/Al0:33Ga0:67As triple barrier resonant tunnelling structures have been studied at low temperatures to investigate the tunnelling electrical behaviour and origin of the current resonances observed in the current-voltage characteristics of these structures. The e�ect of charge accumulation in the emitter quantum well has been investigated, and has been found to signi�cantly alter the behaviour of the electrical characteristics of the structures. These investigations have provided a thorough understanding of the behaviour of these structures and has allowed for optimisation of the triple barrier design with a view to being utilised as a high frequency emitter. The current-voltage characteristics have also been studied as a function of temperature and a novel temperature dependent resonant tunnelling mechanism has been observed. The magnitude of the observed current resonance, which is associated with the energetic alignment to the n = 1 quasi-bound subband states increases with increasing sample temperature which is rare behaviour in systems dominated by quantum mechanics. Finally, the maximum oscillation frequency and output power of these resonant tunnelling structures has been calculated and an optimised triple barrier structure in which charge accumulation in the emitter quantum well does not occur has been designed. Simulated current-voltage characteristics for this design shows it improves the maximum oscillation frequency and maximum output power reported in current state of the art double barrier resonant oscillator structures.

The design of novel solutions for packaging and integration of power semiconductor devices to deliver switches with advanced performance and reliability is very important aspect of power electronics technology evolution. The advancement of technology in this area is committed to bring significant improvements in the design and implementation of power converters particularly in the enhancement of efficiency, higher power density and better cooling system as compared to the state-of-the-art solutions. A power module is a combination of either multiple semiconductor or discrete devices which are connected to form an electrical circuit of certain structure. They are mainly constructed with a stack of four main parts (power semiconductor devices, insulating substrate with circuit conductor, baseplate, and interconnecting material encapsulated in a plastic case) and each of these parts is of a different material. Some of the interfaces within the module are prone to failure with thermal cycling such as wire-bond, solder die attach and substrate. Therefore reducing the number of interfaces in the assembly will greatly reduce the thermal resistance from the junction to ambient and yields noticeable increase of performance. Moreover, using solid posts as opposed to wires to connect the surface of vertical power components enable a significant improvement in power density as compared with standard modules based on wire bond technology. Additionally, the replacement of wires with such posts drastically reduces the distributed parasitic inductance, together with double-sided cooling of the devices, results in an increase of performance and reliability of the components and assemblies. In this work, 70um thick Infineon technology power devices which are rated at 600V/200A were used for the assembly of a Bi-directional switch based converter and discussing the challenges and trade-offs related to selecting processes and materials. Encapsulation is also one of the important factors in making of power module to protect the power chip and the interconnections from moisture, chemicals, dust, gases, and so on. Here, insulation process was carried out for a given prototype using silicone gel; however, it is worth to note the existing challenge on insulating a very small gap between the sandwich layers of the prototype as compared with the standard planar power module structure. A basic partial discharge test was also taken to demonstrate the performance of the insulation. This research has presented an advanced modular integration approach for power device packaging demonstrating the progress beyond the state of the art in power system assembly by proposing a solution which significantly improves electromagnetic and thermomechanical performance of the power module. In particular, fully bond wireless, double sided cooling and layout symmetry are key aspects. The proposed approach is transferable to many topologies having extra benefit of restricting the impact of single device or switch failure on the general system accessibility.

The aerospace and marine sectors are currently using or actively considering the use of DC networks for electrical distribution. This has several advantages: higher VA rating per unit volume of cable and ease of generator connections to the network. In these systems the generators are almost exclusively ac generator (permanent magnet or wound field synchronous) that are linked to the dc network via an electric converter that transforms the ac generator output voltage to the dc rail voltage.The main objective of this project is to develop a Homopolar DC Generator (HDG) that is capable of generating pure DC voltage and could therefore remove the need for an electric converter and ease connection issues to a dc electrical distribution network. The project aim is to design, build and test a small technology demonstrator, as well as electromagnetic modeling validation.In Chapter 1, the initial generator concepts proposed to fulfill the aforementioned requirements of DC generator are presented, as well as an obscurity in electromagnetic induction law faced at the beginning of this project. Also the advantages, disadvantages and different applications of Homopolar DC Generators are covered in Chapter 1. In Chapter 2, Faraday's law of induction and the ways of using it properly are discussed using some example. The preliminary design calculations to construct the prototype HDG are presented in Chapter 3. Also the prototype construction and assembly procedure are discussed in this chapter. In this project, magnetostatics and current flow Finite Element (FE) simulations were used to assess the prototype HDG. In Chapter 4, the results of 2D and 3D-FE simulation are presented; furthermore the limitations of the FE simulations to assess the HDG performance are included. In Chapter 5, the results of the practical tests are demonstrated and assessed, as well as comparison between some of the results obtained practically and those obtained using FE-modeling. Using sliding contacts in the HDG is obligatory so some definitions corresponding to electrical contact resistances are given in Chapter 5. Final chapter is conclusions including the results assessments, future works to design, simulation and construction of the HDG.

Ferroresonance is a nonlinear phenomenon that could cause damage in the power systems equipment due to a high voltage and current during its sustained period. If the system is under sustained ferroresonance for a long time, it can cause thermal damage to the equipment. Therefore, it is important to eliminate or mitigate ferroresonance. It is shown that different mode of ferroresonance gives different impact to power systems. Thus, being able to detect and classify ferroresonance according to its mode during the transient period could avoid the system from going into the sustained period by initiating appropriate mitigation or elimination procedures. The objective of this research is to develop numerical algorithms for ferroresonance monitoring by analyzing its voltage and current signals using Fourier transform and wavelet transform. The aim of this research is to provide features that can be used in the development of a real time monitoring system that may be incorporated in mitigation or elimination procedures in the future. Ferroresonance voltage and current signals are obtained from the modelling of the ferroresonance circuit in the transient program. The sensitivity studies are performed to obtain different modes of ferroresonance and to observe the sensitivity of ferroresonance towards its initial condition and parameter variation. The signals are then being analyzed using Fourier transforms and wavelet transforms to obtain features that can be used in the classification process. Both the sustained and transient periods of the ferroresonance signals are analyzed. The results show that the ferroresonance voltage signals during sustained period are able to be classified according to their modes, however, the ferroresonance signals of the transient period requires further analysis. The algorithms are tested on the real data and produce the similar results that validate the algorithms.

While large-scale wind farms and solar power stations have been used widely as supplement to the nuclear, fossil fuels, hydro and geothermal power generation, at smaller scales these resources are not reliable to be used independently and may result in load rejection or an over size design which is not cost effective. A possible solution to solve this issue is using them as part of a hybrid power system. Complexity in design and analysis of hybrid renewable energy systems (HRES) has attracted the attention of many researchers to find better solutions by using various optimisation methods. Majority of the reported researches on optimal sizing of HRES in the literature are either only considering one objective to the optimisation problem or if more than one objective is considered the effect of uncertainties are ignored. This dissertation work investigates deterministic and stochastic approach in design of HRES. In deterministic approach it shows how adding a battery bank to a grid connected HRES might result in more cost effective design depending on different grid electricity prices. This work also investigates the reliability of HRES designed by conventional deterministic design approach and shows the weakness of common reliability analysis. To perform the stochastic approach the renewable resources variation are modelled using time series analysis and statistical analysis of their available historical meteorological data and the results are compared in this work. Chance constrained programming (CCP) approach is used to design a standalone HRES and it is shown that the common CCP approach which solves the problem based on the assumption on the joint distribution of the uncertain variables limits the design space of problem. This work then proposes a new method to solve CCP to improve the size of design space. This dissertation comprises multi-objective optimisation method based on Non-dominated Sorting Genetic Algorithm (NSGA-II) with an innovative method to use CCP as a tool in estimating the expected value of the objective function instead of Monte-Carlo simulation to decrease the computational time.

Wind energy is planned to play a major role in UK and Scottish Governments achieving renewable energy targets. The Southern Uplands of Scotland are a prime resource for wind and also home to the Eskdalemuir seismological station, a component of the International Monitoring System of the Comprehensive Nuclear-Test Ban Treaty. Previous work demonstrated that large wind turbines generate vibrations at frequencies significant to Eskdalemuir which are transferred into the ground and can be detected at many kilometres. In order to protect its capabilities, a 50 km consultation zone is enforced around Eskdalemuir for all new wind turbine developments, regardless of size. In this thesis, an integrated approach combines multiphysics modelling and seismic monitoring to characterise the vibrations from small wind turbines ( < 50 kW) to assess their effect on Eskdalemuir. Four wind turbines, differing in power, hub height and tower structure, have been monitored using a combination of accelerometers and seismometers attached to the tower and buried in the ground at distances up to 200 m from the turbine. Surface waves are shown to be the predominant wave type originating from the turbines; however, body waves are also present. The waves attenuate at a rate inversely proportional to the distance from the turbine, confirming that the sensors lie within the near-field radiation zone of the tower. Wind speed is shown to affect the tower vibration amplitude differently for each turbine. Visualisation of the bending modes and radiation patterns in the ground have been obtained through multiphysics modelling and this, together with seismic monitoring, has permitted the frequency peaks in the monitored spectrum to be identified as originating from either the turbine or an alternative source. Importantly, it has been shown that the algorithm currently used to assess wind farm vibrations around Eskdalemuir may not be suitable for small wind turbines.

Photovoltaics are used for the direct conversion of sunlight into electricity. In order to provide useful power, the individual solar cells must be connected together. This electrically connected and environmentally protected unit is termed a photovoltaic (PV) module. The structure of a PV module consists of a number of layers of various materials with different properties. The encapsulation material is one of the critical components of a PV module. It mechanically protects the devices and electrically insulates them, ideally for at least the 20-25 year lifetime of the modules. The lifetime of a PV module is generally limited by the degradation of the constituent parts. The materials degrade and cause a decrease in the efficiency leading to eventual failure, with the encapsulant being particularly susceptible to degradation. The most common encapsulant material is Ethylene Vinyl Acetate (EVA) the degradation of which leads to a significant drop in a PV module’s efficiency, durability and lifetime. EVA undergoes chemical degradation when it is exposed to environmental factors such as elevated temperature, humidity and Ultra Violet (UV) radiation. Although numerous works have been done in this field there is still a gap in knowledge to fully understand the degradation of EVA and develop a predictive tool. This work investigates the chemical degradation of an EVA encapsulant to understand the degradation mechanisms, develop a predictive model and correlate the degradation with changes in the structure and mechanical properties. To determine the effect of environmental stresses on EVA environmental conditions were simulated in the laboratory in order to accelerate the test program. The ageing was classified into three main groups, namely thermal ageing, UV ageing and damp-heat ageing. In order to investigate the effect of elevated temperature on the mechanical and thermal properties and also to study the thermal degradation, EVA sheets were aged in a dark laboratory oven at 85°C for up to 80 days. To investigate the impact of UV exposure on the properties and photodegradation of EVA the samples were exposed to UV radiation of 0.68 W/m2 at 340 nm and 50°C. To study moisture diffusion and the impact of absorbed moisture on the mechanical properties and morphology, EVA sheets were aged in an environmental chamber at 85°C-85% RH and using a potassium chloride (KCl) salt solution in a sealed chamber to obtain 85% RH at room temperature (22±3°C). Thermal analysis techniques including Differential Scanning Calorimetry (DSC), Thermo-gravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA) along with Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Gravimetrics were used to investigate the structure, degradation kinetics and viscoelastic mechanical properties of the EVA as a function of ageing. The EVA was shown to have viscoelastic properties that were highly sensitive to the ambient temperature. Thermal ageing was shown to reduce the storage modulus due to the changes in the structure of the EVA and reduction in crystallinity. Over a longer time, chemical changes due to thermal activation also occurred, hence, these were insignificant compared with transient thermal effects. The activation energy of deacetylation was also shown not be affected by the ageing process. Investigation of photodegradation showed notable chemical changes as a result of UV exposure, with FTIR absorbance peaks related to carboxylic acid, lactone and vinyl exhibiting a sharp increase after UV irradiation. Differences in the ATR-FTIR spectra of the UV irradiated and non-irradiated samples showed that the intensity is depth dependant. DMA results showed UV ageing had a significant influence on the mechanical properties of the EVA and reduces the storage modulus. The predictive photodegradation model showed a good agreement on the UV irradiated surface with the experimental data where it did not agree well with the results on the non-irradiated side which could be due to the presence of UV absorber. The response of the EVA to damp heat was investigated at two conditions with same the RH level (85% RH) and different temperatures (room temperature and 85°C). The moisture diffusion coefficient was measured via gravimetry and Water Vapour Transmission Rate (WVTR) technique which were well-agreed. Results from DSC indicated that the crystallinity increased due to incorporation of moisture into the structure of the copolymer but decreased as ageing continued, showing the significant influence of elevated temperature and thermal degradation on the structure of EVA. A comparative study of the impact of the ageing on the structure and mechanical properties indicated that UV has a stronger degrading influence comparing to other degradation factors. DSC results also suggested that property changes could be connected to structural modifications. The impact of different degradation factors can be summarised as UV > T > DH.

The microgrid concept integrates Renewable Energy Systems (RES) to the Electrical Power System (EPS) as a means to produce clean energy, meet consumer energy demands and preserve the depleting fossil fuels reserves. These RES are usually interfaced to the grid using power electronic converters (such as Voltage Source Converters) to achieve the required control and conversion of power. Nevertheless, Voltage Source Converters (VSCs) produce both current and voltage harmonics which negatively impact on the Power Quality (PQ) of a microgrid and may cause damage or malfunctions of equipment. This thesis focuses on the impact of VSC harmonics on the power quality of a microgrid. It also investigates various factors that affect the harmonics generated by VSCs with the aim of predicting their impact on the PQ of the microgrid. The PQ of the microgrid is represented as a measure of the level of harmonic distortion of the voltage and current at the Point of Common Coupling (PCC) to the grid. The harmonic mean was used as a measure to determine if the VSCs harmonic level meets the IEEE Standard 519 harmonic limits. The level of harmonic distortion of many VSCs can be significantly affected and difficult to predict in the presence of uncertainties, which may arise due to design parameter choice or system parameter changes. This necessitates the use of statistical techniques to quantify VSC harmonic distortion level in the presence of uncertainties. A common statistical approach is to employ Monte Carlo Simulation (MCS), although accurate it is time consuming and burdensome for systems containing a large number of variables. This thesis utilizes the Univariate Dimension Reduction (UDR) technique formulated from an enhanced Unscented Transform (UT) equation in predicting the harmonic distortion level of large numbers of VSCs in a microgrid, when some system or design parameters are only known within certain constraints. The UDR technique drastically reduce the computation time and burden associated with the MCS approach and avoids assumptions that leads to system simplification required to implement other analytical methods. Various microgrid configuration and statistical distributions similar to practical system variations of RES are considered in order to achieve a good evaluation of the UDR performance in predicting the VSC harmonics. The UDR performance was also evaluated experimentally using a practical microgrid lab containing 3 VSCs. The MCS approach was used as a benchmark for the predicted UDR results. In all cases the UDR predicted results were obtained with significant time saved as compared to the MCS approach and the UDR results showed a good match with the MCS approach.

Nowadays the production of energy originating from renewable sources is a burning issue, in particular a lot of efforts are made for a reduction of worldwide energy consumption for a sustainable world. The efficient and low-cost direct conversion of solar photons into electricity is one of the most important scientific and technological challenges of this century. Up to now, commercially available photovoltaic technologies are based on inorganic materials, which require high costs and highly energy consuming preparation methods. Organic photovoltaic can avoid those problems, but the best efficiencies of organic-based photovoltaic cells are at the moment around 7%. Dye-sensitised solar cells (DSSCs) represent a concrete solution for harnessing solar energy and converting it into electrical energy and 11% efficiencies have been reached with the most performing Ru(II) sensitizers, such as N3 (cis-di(thiocyanato)bis(2,2- bipyridyl-4,4′-dicarboxylate) ruthenium(II)) and N719 (bis(tetrabutylammonium)-cisdi(thiocyanato)-N,N′-bis(4-carboxylato-4′- arboxylic acid-2,2′-bipyridine) ruthenium(II)). The photosensitiser dye plays a strategic role in DSSCs, absorbing the solar light and promoting the formation of an electron-hole pair which is eparated, transported, and then collected at the electrodes. Other organometallic complexes have also been used as dyes in DSSCs, for examples complexes of Pt(II), Fe(II), Os(I), Cu(I), Re(I) and Ir(III). Iridium complexes are potentially good candidates for application in DSSCs. The absorbed photon to current yield in iridium based DSSC devices is comparable to the ruthenium dyes. Moreover, the ruthenium dyes produce current only by injection from metal to-ligand charge transfer (MLCT) states whereas, for iridium dyes, it would be possible to combine injection from both MLCT and ligand-to-ligand charge transfer (LLCT). However, up to now, low molar extinction coefficient and a narrow absorption spectrum at relatively high energy (380 nm) are critical factors that limit the efficiency of Ir(III) dyes. For this reason, the reported DSSCs solar cells based on Ir(III) complexes are characterized by low efficiencies. In this thesis, I present my results on the design and synthesis of new dyes for DSSC application. Described in Chapter 2 is the synthesis of iridium (III) complexes where aryl-1,2,3- triazole ligands act as cyclometalating ligand and 4,4‟-dicarboxy-bipyridine as N^N ancillary/anchoring ligand. The photophysical effects of these complexes were investigated. It was found that by using different substituents on the phenyl ring, or a different aryl system, it is possible to tune the absorption and the emission of these complexes. Computational studies showed HOMO-LUMO directionality of these complexes is ideal for the electron injection once they are applied on DSSC devices. Preliminary efficiency test have been carried out with promising results. Described in Chapter 3 is the synthesis of iridium (III) complexes designed as dyes for p-type DSSC. For these complexes a phenylpyridine containing a carboxylic group has been used as cyclometalating/anchoring ligand whereas different diimine ligands act as ancillary ligands. The photophysical effects of these complexes were investigated. It was found that using different π-systems on the ancillary ligand is possible to tune the absorption of these complexes and to enhance the spatial separation between HOMO and LUMO. Computational studies confirm the potential use of these complexes on DSSC devices. Preliminary tests on NiO devices have been carried out. Described in Chapter 4 is the synthesis of a novel bipyridine-1,2,3-triazole based anchoring group. The novel triazole ligand might act as spacer between the metal oxide and the metal center insulating the electronic coupling and avoid the recombination. This N^N ligand, obtained through click of azido-bpy and acetylenedicarboxylate, was used as an anchoring ligand in ruthenium, iridium and rhenium complexes. The set of three metal complexes was compared with their dicarboxybipyridine analogues. Looking at the photophysical and electronic properties of these new complexes they seem comparable with their dicarboxybipyridine analogues. Preliminary anchoring tests on TiO2 have been carried out. Described in Chapter 5 is the design and synthesis of two cyclometalated Ir(III)– coumarin molecular arrays, which show intense absorption of visible light, one belonging to p-type dyes family and another belonging to n-type one. The two complexes have been characterised and tested on both TiO2 and NiO cells.