Most of our energy supply nowadays relies on converting thermal energy to mechanical energy. Mechanical energy is then either used directly to drive vehicles or electric generators that supply the global needs of electricity. The main source of thermal energy is combustion of fossil fuels, which are limited, and have many detrimental effects on polluting the environment and adding to the greenhouse effect. Fuel cells offer the best alternative to replace existing energy conversion processes, as they convert the chemical energy of hydrogen fuel directly into electricity, bypassing fuel combustion. In addition, the only by-products in fuel cells are water and low temperature heat, and both are benign to the environment. Being a single step energy converting devices, fuel cells have high efficiencies. However, the fuel cell outputs unregulated voltage that depends on the operating conditions of the fuel cell and the load connected across its terminals.

The primary outcome of this research project is the development of a methodology enabling fast automated early-stage power and energy analysis of configurable processors for system-on-chip platforms. Such capability is essential to the process of selecting energy efficient processors during design-space exploration, when potential savings are highest. This has been achieved by developing dynamic and static energy consumption models for the constituent blocks within the processors. Several optimisations have been identified, specifically targeting the most significant blocks in terms of energy consumption. Instruction encoding mechanism reduces both the energy and area requirements of the instruction cache; modifications to the multiplier unit reduce energy consumption during inactive cycles. Both techniques are demonstrated to offer substantial energy savings. The aforementioned techniques have undergone detailed evaluation and, based on the positive outcomes obtained, have been incorporated into Cascade, a system-on-chip coprocessor synthesis tool developed by Critical Blue, to provide automated analysis and optimisation of processor energy requirements. This thesis details the process of identifying and examining each method, along with the results obtained. Finally, a case study demonstrates the benefits of the developed functionality, from the perspective of someone using Cascade to automate the creation of an energy-efficient configurable processor for system-on-chip platforms.

Smart power supply grids may be required to link future energy production and consumers. Multilevel converters are a building block for smart grids. There are several structures of multilevel converters, for example the Neutral Point Clamped (NPC), the Flying Capacitor Circuit and the Cascaded H-Bridge (CHB) converter. The modular structure of the CHB multilevel converter makes it one of the best options for smart grids. Using modular converter structures reduces production and maintenance costs. Implementation of efficient and fast controllers for multilevel converters requires accurate measurement of the voltages and currents for the system feedback loops. Knowledge of the DC link voltages is necessary to construct voltage control loops. In a typical CHB multilevel converter there are many DC links which means that a lot of voltage transducers maybe required. Voltage transducers at medium voltage are not easy to implement and add to system cost. This thesis presents an efficient way to observe the DC link voltages and hence eliminate the cost associated with voltage transducers. A “Sliding Mode Observer (SMO) using the Equivalent Control Method” has been chosen because of its robustness against system uncertainties. Simulation and practical work has been performed on a three-phase, three-cell multilevel converter to validate the use of this observer.

Nowadays, power electronic converters based exclusively on IGBTs seem to have achieved excellent load side performance up to megawatt powers range in the low voltage range (200-690Vrms) and are steadily gaining good performance in the medium voltage range as well. However, the medium and high voltage/high power range remains dominated by converters using naturally commutated thyristors, such as line-commutated cycloconverters, line-commutated current source inverters, which provide comparatively poorer output side performance. The purpose of this thesis is to investigate both the conventional cycloconverter, which will be referred as standard cycloconverter in the thesis, and the new hybrid cycloconverter topologies, which are capable of improving the performance of the standard cycloconverter by adding an auxiliary forced commutated inverter with reduced installed power. It will be shown that the new topology is not only able to improve the quality of the output voltage, but also to enhance the control over the circulating current and therefore, for some of the standard cycloconverter arrangements, to improve the input power quality. To realize the evaluation of the standard cycloconverter and validate the feasibility of the new hybrid cycloconverter in both circulating current and circulating current-free mode, SABER simulation models are developed in the first place to perform the initial analysis. A configurable three-phase input to three-phase output cycloconverter prototype which can be easily changed via a switch box to test four different cycloconverter topologies (standard and hybrid) is designed and implemented in the laboratory. Finally, the whole system is debugged and tested. All the relevant results obtained from both the simulation and experiment will be thoroughly analyzed in the thesis.

Energy is potentially at the hub of modern civilization and right from Industrial Revolution, technology has refined and redefined the way we use energy; but technological advancement in all spheres will continue to depend and use energy to progress. However, fossil fuels (coal, gas, oil) have remained the dominant energy resource accounting for a larger proportion of world energy consumption when compared to nuclear energy and renewable energy resources. There are mounting fears of both the climate and our environment reaching a characteristic tipping point due to global warming. This is associated with the relentless use of fossil fuels and uncontrolled emissions of greenhouse gases. The persistent trend has triggered the need for alternative and renewable energy options which are now being considered and pursued globally to avert the possibility of climate change attaining a state of irreversibility. This research describes the development of a novel 2kWe biomass fired Organic Rankine Cycle (ORC) system intended for remote off-grid locations, employing a multi-vane expander as the prime mover. The expander is a four vane model 6AM-FRV-5A 3kW Gast Air motor manufactured by Gast Manufacturing Inc. The prime mover will harness power produced by high pressure vapour to generate torque and rotational motion on the shaft and the mechanical energy generated is converted to electricity by means of an automotive alternator. The conversion of low and medium temperature heat from biomass to electricity by using low cost, lightweight and low maintenance expander as well organic substances or hydrofluoroether, HFE 7100 and HFE 7000 is the subject ofthis research. In order to assess and predict the performance of the system an EES simulation of a basic cycle is carried out in order to compare the the outcome with the actual cycle. A preliminary air test of the system was also carried out to have a perspective on actual performance using compressed air. However, the organic substance, hydrofluoroether (HFE) to be used in further tests is selected because of its thermodynamic properties of having a lower specific volume and higher molecular weight than steam allowing for smaller, less complex, less costly energy applications like expanders and smaller diameter tubes to be employed for low temperature micro system. This is achieved through a phase change transformation in a Rankine cycle process between specified temperature limits when compared to turbines which operate at higher temperature and pressure. An experimental study and initial testing is carried out using a Chromalox- Model CES-12, 9 kW boiler providing temperatures between 100oC and 115oC and test measurements collated and analysed to predict performance and assess outputs and possibly fluctuations in the system. A test involving the use of the biomass boiler is carried out later and analysed results compared with that of the electric boiler. The process will involve the supply of heat from the biomass boiler and the high pressured vapour generated in the ORC cycle is expanded through the prime mover with a fall in temperature and pressure at the exhaust and exiting as saturated vapour or a mixture of vapour and liquid. The energy stored in the working fluid in the vapour state is converted to electricity by work on the shaft while the exhaust heat can be tapped for domestic uses as thevapour is expanded down to low pressure in the condenser and the saturated liquid is pumped to a high pressure in the evaporator to resume the cycle.

At present there is much debate about the impacts and benefits of increasing the amount of generation connected to the low voltage areas of the electricity distribution network. The UK government is under political pressure to diversify energy sources for environmental reasons, for long-term sustainability and to buffer the potential insecurity of uncertain international energy markets. UK Distribution Network Operators (DNOs) are processing large numbers of applications to connect significant amounts of Distributed Generation (DG). DNOs hold statutory responsibility to preserve supply quality and must screen the DG applications for their impact on the network. The DNOs often require network upgrades or DG curtailment, reducing the viability of proposed projects. Many studies exist that identify barriers to the widespread connection of DG. Among them are: suitability of existing protection equipment; rating of existing lines and equipment; impact in terms of expanded voltage envelope and increased harmonic content; conflict with automatic voltage regulating equipment. These barriers can be overcome by expensive upgrades of the distribution network or the expensive deep connection of DG to the higher voltage, sub-transmission network. This work identifies changes in network operating practice that could allow the connection of more DG without costly upgrades. The thesis reported is that adopting options for a more openly managed, actively controlled, distribution network can allow increased DG capacity without upgrades. Simulations have been performed showing DG connected with wind farm production time series to a representative section of the Scottish distribution network. The simulations include modelling of voltage regulation by network equipment and/or new generation. The cost and effects of the consequent network behaviour evaluated in monetary terms are reported. Alternative control strategies are shown and recommended, to reduce DNO operation and maintenance costs and the cost of connection to the developer with no reduction in supply quality.

No description available.

In this thesis various mathematical methods of studying the transient and dynamic stabiIity of practical power systems are presented. Certain long established methods are reviewed and refinements of some proposed. New methods are presented which remove some of the difficulties encountered in applying the powerful stability theories based on the concepts of Liapunov. Chapter 1 is concerned with numerical solution of the transient stability problem. Following a review and comparison of synchronous machine models the superiority of a particular model from the point of view of combined computing time and accuracy is demonstrated. A digital computer program incorporating all the synchronous machine models discussed, and an induction machine model, is described and results of a practical multi-machine transient stability study are presented. Chapter 2 reviews certain concepts and theorems due to Liapunov. In Chapter 3 transient stability regions of single, two and multi~machine systems are investigated through the use of energy type Liapunov functions. The treatment removes several mathematical difficulties encountered in earlier applications of the method. In Chapter 4 a simple criterion for the steady state stability of a multi-machine system is developed and compared with established criteria and a state space approach. In Chapters 5, 6 and 7 dynamic stability and small signal dynamic response are studied through a state space representation of the system. In Chapter 5 the state space equations are derived for single machine systems. An example is provided in which the dynamic stability limit curves are plotted for various synchronous machine representations. In Chapter 6 the state space approach is extended to multi~machine systems. To draw conclusions concerning dynamic stability or dynamic response the system eigenvalues must be properly interpreted, and a discussion concerning correct interpretation is included. Chapter 7 presents a discussion of the optimisation of power system small sjgnal performance through the use of Liapunov functions.

This thesis presents a study of two outstanding problems in eddy-current coupling theory: (a) the steady-state performance of copper-faced couplings. (b) the transient performance of eddy-current couplings. After a general introductory chapter which reviews the problems of coupling analysis and existing theories of the machine, the work falls, broadly, into two parts. The first part (chapters 2-4) presents a three-dimensional theory of the copper-faced coupling and describes experiments designed to test the validity of the theory. The second part (chapters 5-9) is devoted to the transient performance of eddy-current couplings; in particular, torque response at constant slip speed. After reviewing existing practice and possible theoretical approaches, a theory, based on the transient solution of the diffusion equation, is developed. Experiments on a new test machine, which investigate the assumptions of the theory and the method of torque prediction, are discussed in detail.

This thesis describes the synthesis and characterisation of conjugated materials, and their optoelectronic applications. The first chapter introduces the concept of solar cells and describes the most common types of solar cells used nowadays, including examples of some of the best performing materials. The second chapter describes the donor-functionalised synthesis of a small library of DPP derivatives with optoelectronic applications. DPP derivatives were used to gain knowledge about the physical parameters contributing to better PCE in organic solar cells, others were used as donors for BHJSC giving a highest PCE of 1.76%. Finally one DPP derivative proved to be an efficient fluoride chemosensor, able to selectively detect fluoride in the presence of other anions by means of colour change (and absorbance in the near infrared), and a change in its 1H NMR spectrum. The third chapter describes the one-pot synthesis of BODIPY molecules that can be further tuned to adjust their photophysical properties. These derivatives were used as donors for BHJSC giving a highest PCE of 0.45%. The absorption and emission properties of the molecules were studied, and it was found that the intensity of the emission depends on the electron richness of the substituent in the meso position. Some derivatives proved not to be fluorescent, whereas others exhibited extremely small Stokes shifts, sometimes as low as 1 nm. Chapter 4 describes the synthesis of a spirofluorene and a copper complex derivative with the aim of preparing molecules that could self-assemble forming 3D networks, in order to improve the dimensionality of the system. Their photophysical properties were studied, and the molecules proved to be fluorescent with large Stokes shifts, sometimes up to 100 nm. Chapter 5 describes the synthesis of fullerene derivatives with optoelectronic properties. One of the most successful derivatives was involved in a supramolecular chemistry study, to investigate how recognition-mediated assembly can lead to effective charge transfer from a quantum dot. Finally Chapter 6 describes a series of dyes synthesised using a simple 2/3 step synthetic pathway. DSSC were fabricated and the best performing dye with a 2 step synthetic route gave a PCE of 2.32%, whereas the best performing dye with a 3 step synthetic route gave a PCE of 4.35%. The high PCE of these types of dyes considering their ease of preparation makes their large-scale synthesis commercially feasible.