Power generation gas turbine manufacturers and operators are tasked increasingly with expanding operational flexibility due to volatility in global gaseous fuel supplies and increased renewable power generation capacity. Natural gas containing high levels of higher hydrocarbons (e.g. ethane and propane) is typical of liquefied natural gas and shale gas, two natural gas sources impacting gas turbine operations, particularly looking forward in the United Kingdom. In addition, hydrogen-blending into existing natural gas infrastructure represents a potential energy storage opportunity from excess renewable power generation, with associated combustion impacts not fully appreciated. This thesis aims to address the specific operational problems associated with the use of variable gaseous fuel compositions in gas turbine combustion through a combination of experimental and numerical techniques, with a focus on natural gas blends containing increased levels of higher hydrocarbons and hydrogen. Parametric experimental combustion studies of the selected fuel blends are conducted in a new fully premixed generic swirl burner at elevated ambient conditions of temperature and pressure to provide representative geometry and flow characteristics typical of a can-type industrial gas turbine combustor. New non-intrusive diagnostic facilities have been designed and installed at Cardiff University’s Gas Turbine Research Centre specifically for the characterization of the influence of fuel composition, burner geometry, and operating parameters on flame stability, flame structure, thermoacoustic response, and environmental emissions. Experimental measurements are supported through the use of numerical chemical kinetics and acoustic modelling. Results from this thesis provide an experimental validation database for chemical kinetic reactor network and CFD modelling efforts. In addition, it informs gas turbine manufacturers on potential burner design modifications for future fuel flexibility and provide enhanced empirical tools to power generation gas turbine operators for increased operational stability, reduced environmental impact, and increased utilization.

Training, education and research on renewable based power systems and automation is the topic of discourse among scientific and academic community. Renewable energy generation technologies are viewed as one of the solution that could significantly contribute to solve the problems associated with global warming and environment destruction. They are clean, available in abundance and distributed in nature. This means, on one side, there are huge solar or wind parks generating energy for large number of households connected over grid and on the other side, there are stand-alone systems capable of satisfying energy requirements of a single household. For efficient operation and control of these systems, trained and educated power system engineers are required. In order to increase acceptability of these systems among common people, awareness regarding the system and its operation is significant. Theoretical and simulation based platforms are useful but not sufficient to deliver power systems education. There is requirement of a platform which would offer opportunity of learning through interaction with real system hardware. It should be affordable, easy to access and familiar to most of the users. The concept should extend further to include a defined learning methodology which could offer the best education value from the experiment. In this thesis, methodology to use the idea of TeleLab (also known as remote lab or web lab) for Hybrid Power System (HPS) with renewables is proposed, implemented and evaluated on the basis of its purpose to offer high educational value to the users and its ability to promote knowledge and technology transfer between users and institutions all over the world. The purpose of this PhD work is to take advantage of remote communication technology like internet to access labs or research facilities/infrastructure to promote power systems education. This work is aimed at developing a TeleLab with focus on renewable based HPS. The knowledge of information technology, automation technology and power systems engineering is used to describe best practice to perform renewable energy experiments from remote location. The remote experiment platform would be cost effective and could be used for technology and knowledge transfer among users located in remotely accessible areas, those with physical disabilities, those representing educational and research institutions and including those who represent professional firms. Resources could be shared between different institutions along with promoting collaborative learning and research activities focused on power engineering education. Development of this remote platform to perform real experiments offer several economic advantages to the users like saving in travel time and costs, saving in infrastructure investments, saving in lab personnel costs, possibility to use the experiment environment with greater flexibility and for longer time. Social advantages offered by this approach to the user are in terms of possibility to establish good work-life balance. Significant benefits are offered for users from developing or poor countries where possibilities of investments in costly lab infrastructure are rare. The thesis discusses scientific contribution to knowledge like design, development and implementation of the hardware structure of HPS consisting of renewable energy technologies like solar and wind supported by battery system. Programmable Logic Controller (PLC) is used to automate the HPS which functions as a “smart system” contributing to the idea of smart grid. It performs operations like reading and recording system parameters, monitoring and control of system components, management of system load and management of battery charging mechanism. This follows by design, development and implementation of TeleLab to monitor and control the system from remote location over internet. This involves the task of development and implementation of safety and security measures related to the proposed system. It was aimed to develop a remote lab which offers high educational value to the user. This was achieved by proposing innovative thinking in designing and development of learning activities on MOODLE learning management system. To facilitate efficient solving of issues related to the lab and to encourage participation of users in the experiment design and development process, a feedback mechanism was proposed. Methodology to analyze, evaluate and assess system as well as user performance assisted by possibility to provide suggestions or guidance for improvement was proposed. The thesis concludes by presenting results about the performance of the HPS using TeleLab platform and its impact over user performance with respect to knowledge and technology transfer. This analysis is performed by evaluating and assessing user performance in comparison to hands-on lab and TeleLab. Economic impact of remote experimentation for users and institutions is discussed in this thesis. At the end, possible future aspects of this concept are discussed.

Photovoltaics (PV) have seen rapid global penetration into the low voltage (LV) electricity distribution grid year-on-year. The result of high PV penetration levels is grid impacts of voltage fluctuations, harmonic distortions and reverse flow among others. Research that attempts to quantify the maximum allowable PV penetration into the LV grid before experiencing detrimental impacts is an important. The most commonly reported barrier to enabling grid impact analysis is the lacking availability of high-resolution and geographically flexible solar irradiance data. As an alternative, synthetically generated solar irradiance data can be used. There is a distinct lack of synthetic solar irradiance generators that can derive high resolution and statistically accurate solar irradiance data using only readily available inputs. This thesis presents the development of two synthetic generators: the Solar Irradiance Generator (SIG), and the Spatially Decorrelating Solar Irradiance Generator (SDSIG). The SIG proves the concept that synthetic minutely irradiance time series can be generated using readily available mean hourly observations of total cloud amount, atmospheric pressure, wind speed and cloud base height. The SDSIG presents the first ever methodology to synthetically generate unique and spatially decorrelating minutely irradiance time series for any number of uniquely orientated and tilted houses inside a spatial domain using the same inputs as the SIG. The SDSIG employs (1) Markov chains, to derive stochastic weather variable time series, (2) synthetic representations of clouds in the sky, using a novel method called cloud fields, (3) globally flexible irradiance estimation models, and (4) distributions of clear-sky irradiance by total cloud amount, to create the irradiance time series. The SDSIG outputs are temporally validated using metrics of ramp rates, variability indices and irradiance magnitude frequencies against real world observations at two UK sites and two USA sites, representing three distinct climates. Daily 2-sample Kolmogorov-Smirnov tests of each metric passed a minimum of 95.34% of the time with a 99% confidence limit. The lowest CDF correlation coefficient between modelled and observed data for all metrics and sites was R=0.908; the mean was R=0.987. The SDSIG outputs are spatially validated at Oahu, HI USA, showing R=0.955, RMSE=0.01 and MAPE=0.865% when comparing modelled and observed spatial correlation versus site separation. The SDSIG outputs are applied to a grid impacts power flow model of an LV grid with increasing PV penetration to test the over voltage metric of daily on-load tap changer (OLTC) operations. Using correlating irradiance time series at each house in the LV grid overestimates OLTC operations in every instance of PV penetration when compared to using spatially decorrelating irradiance time series from the SDSIG.

The popularity of the Internet and the demand for 24/7 services uptime is driving system performance and reliability requirements to levels that today’s data centres can no longer support. This thesis examines the traditional monolithic conventional server (CS) design and compares it to a new design paradigm known as disaggregated server (DS). The DS design arranges data centres resources in physical pools such as processing, memory and IO module pools; rather than packing each subset in a single server. In this work, we study energy efficient resource provisioning and virtual machine (VM) allocation in the DS based data centres compared to CS based data centres. First, we developed a mixed integer linear programming (MILP) model to optimise VM allocation for DS based data centre. Our results indicate that considering pooled resources yields up to 62% total saving in power consumption compared to the CS approach. Due to the MILP high computational complexity, we developed an energy efficient, fast and scalable resource provisioning heuristic (EERP-DS), based on the MILP insights, with comparable power efficiency to the MILP. Second, we extended the resources provisioning and VM allocation MILP to include the data centre communication fabric power consumption. The results show that the inclusion of the communication fabric still yields considerable power savings compared to the CS approach, up to 48% power saving. Third, we developed an energy efficient resource provisioning for DS with communication fabric heuristic (EERP-DSCF). EERP-DSCF achieved comparable results to the second MILP and with it we can extend the number of served VMs where the MILP scalability for big number of VMs is challenging. Finally, we present our new design for the photonic DS based data centre architecture supplemented with a complete description of the architecture components, communication patterns and some recommendations for the design implementation challenges.

The small-scale wind turbine is considered as one of the most effective renewable technologies due to their potential to provide useful amount of electricity, particularly in ‘‘off-grid’’ settings as well as promising future prospects to decarbonise the power sector and ultimately stabilise energy security. Due to the huge potential of the wind resources and financial incentives, the UK is a promising region for small-scale wind energy development but there has been lack of comprehensive assessment of the wind resource for relevant locations. Thus efficient and low cost techniques are urgently needed to assess the resource potential since the long-term measurement techniques usually employed in the large-scale industry are very expensive and often not feasible for small-scale development. The research developed during this thesis focuses on cost effective techniques for predicting the wind resource using two main approaches, namely the boundary layer meteorology and measure-correlate-predict (MCP). These approaches were evaluated using a long-term dataset from the Modern Era Retrospective-Analysis and short-term onsite dataset from meteorological measurement station. To begin with, the performance of a modified methodology based on the boundary layer meteorology was evaluated at four UK sites, and the results were validated using traditional error metrics. Averaged across all sites, the percentage error in the predicted wind power density was found to be about 25% due to the uncertainties associated with the choice of the input parameters. Although the result is very encouraging, it was concluded that such a method is better applied in a ‘‘preliminary’’ analysis to identify viable sites worthy of further investigation. To reduce these uncertainties, an MCP technique was utilised along with onsite measurements over a period of 12 months at a subset of 1 of the 4 UK sites, and the results show a significant improvement on the predicted wind speed and power density. Comparison of both approaches show that the best performing MCP approaches resulted in percentage error in the predicted mean wind speed and power density of 7.2 % and 12.9 % in contrast to the 18.9 % and 17.0% obtained using the boundary layer approach. Seasonal trends, direction behaviours and frequency distribution were analysed and their characteristics reflected the general wind conditions across most UK sites. Based on the output of the wind resource assessment, the potential of a small-scale vertical axis wind turbine (VAWT) was assessed using the double multiple streamtube model. VAWTs based on the Darrieus concept are potentially more efficient and economical, but those with fixed pitch blades are inherently non self-starting and are unsuitable for decentralised application. It is shown that the self-starting problem can be alleviated by a combination of a suitable aerofoil sections, solidity and pitch angles. The thesis provides a technique for inexpensive wind resource assessment where direct long-term measurements are not feasible. In addition, it provides a suitable solution strategy to the problem of self-starting in small-scale fixed pitch wind turbines.

The electrical properties of evaporated vitreous selenium layers have been studied using both the injection and volume-generation of additional charge carriers. The current-voltage characteristics of specimens between 2 and 31mum thick were investigated and the results analysed in terms of the Rose-Lampert theory. Ohmic contacts of tellurium or platinum were formed on newly prepared specimens by the prolonged application of a moderately high electric field, but this was not found possible with a low work function electrode such as magnesium. The detailed analysis of the results indicates the existence of a volume distribution of hole traps of density 9 x 1013 cm.;-3; 0.79 eVabove the valence band. The comparative shallowness of the characteristics at higher voltages suggests that this level forms part of a distribution of states increasing in density towards the valence band. It is shown that the model of an exponential trap distribution is consistent with the experimental results and also leads to an explanation of the unusual optical properties of vitreous selenium. Measurements of the transient response of carriers generated by pulses of light or high energy electrons show the traps in the 0.79 eV level have a release time of about 50 seconds at room temperature and a capture cross-section for holes of 8 x 10.;-16 cm2. The lifetime of voltage injectedholes with respect to these centres is about 10? seconds. On the basis of the electrical results, both the absorption and photoconductive edges have been calculated as a function of the photon energy and it has been possible to account for the marked energy difference between the two. The interpretation shows that at room temperature the band gap for vitreous selenium is 2.45 eV. Band models of selenium are briefly reviewed and it is suggested that the trap distribution is most likely connected with chain ends.

This thesis considers control system enhancement for Wave Energy Converters (WECs), of the point-absorber type, used for water desalination. The thesis makes several contributions. Firstly, it is shown that a type of nonlinear control system previously used in the literature provides global stability guarantees for this type of WEC in the absence of input constraints. Following this, several anti-windup techniques for a certain class of nonlinear systems with input constraints are developed; a nonlinear Internal Model Control (IMC) compensator, a linear reduced-order compensator and a linear sub-optimal performance compensator. It is shown how these anti-windup strategies are natural generalisations of those found elsewhere in the literature and how all of these compensators can be designed such that global exponential stability of the class of systems considered is guaranteed. Finally, the thesis describes the application of these anti-windup techniques to a nonlinear simulation model of a WEC system where their benefits are clearly demonstrated. It is shown that these compensators improve the performance of the WEC during periods of saturation and, moreover, that the sub-optimal compensator can achieve desirable tracking without causing any damage to the desalination equipment. These results demonstrate the benefit of anti-windup for WEC control and imply potential savings in terms of operation and maintenance costs, thereby contributing to the potential commercialisation of such devices.

Radial junction nanowire solar cells are expected to give a higher performance than planar junction solar cells. This is due to the enhanced optical path length for absorption, and the shorter distance for excitons to travel to interfaces where they can dissociate. By means of simulation, we have optimised, with respect to geometrical parameters, solar cells consisting of light absorber coated metal- oxide nanowires. We have primarily studied nanowires with a TiO2 core and CdSe shell, as well as ZnO cores with PbS nanoparticles. Optical scattering and absorption is determined using Finite-Difference Time-Domain (FDTD) simulations. Charge transport is studied using finite-difference drift-diffusion modelling. The generation rate calculated from FDTD is inputted into the charge transport model. The aim is to determine which combination of nanowire parameters (such as coating thickness, height, radius and spacing) lead to the the highest power efficiencies. We found that core and shell thickness has more effect on absorption than nanowire arrangement.

With the power system evolving from passive to a more active system there is an incorporation of information and communication infrastructures in the system. The measurement data are more prone to tampering from attackers for mala fide intentions. Therefore, security and reliability of distribution have become major concerns. State estimation (SE), being the core function of the energy/distribution management system (EMS/DMS), has become necessary in order to operate the system efficiently and in a controlled manner. Although SE is a well-known task in transmission systems, it is usually not a common task in unbalanced distribution systems due to the difference in design and operation philosophy. This thesis addresses these issues and investigates the distribution system state estimation with unbalanced full three-phase modelling. The formulation, based on weighted least squares estimation, is extended to include the open/closed switches as equality constraints. This research then explores the vulnerabilities of the state estimation problem against attacks associated with leverage measurements. Detecting gross error particularly for leverage measurements have been found to be difficult due to low residuals. The thesis presents and discusses the suitability of externally studentized residuals compared to traditional residual techniques. Additionally, the masking/swamping phenomenon associated with multiple leverages makes the identification of gross error even more difficult. This thesis proposes a robust method of identifying the high leverages and then detecting gross error when the leverage measurements are compromised. All algorithms are validated in different IEEE test systems.

The offshore wind resource around the seas of the UK is a very large renewable energy resource. Future offshore wind farm sites leased by the Crown Estate for Round 3 development will need high power capacity grid connection, but their remote location presents a challenge for the electrical connection to the grid. Long distance AC cable transmission is not practical due to the large cable capacitance which leads to reactive power loss. This thesis considers the voltage source converter and high voltage direct current (VSC-HVDC) technology as the future grid connection for the offshore wind farm network, which is more controllable and has better transmission efficiencies for long distance and high power cable transmission applications. The offshore AC network is weak with very little inertia and has limited rating at the HVDC converter substation. The dynamics in key variables in the offshore wind farm AC network and how they affect certain components in the system were studied. Without proper control, the offshore voltage and the frequency will be sensitive to change. The capacitor of the AC filter at the offshore VSC-HVDC station was found to be vulnerable to over-voltage, therefore a closed loop AC voltage controller was proposed here to maintain a constant capacitor voltage and to prevent tripping or over-voltage damage. The tuning of the control gains were optimised with a pole placement design method and small signal analysis for observing the system eigenvalue damping. The control parameters were then tuned for a fast and well damped controller. The AC voltage controller was evaluated and compared to an open loop system. The controller was able to limit the resonance in the LC filter that can be triggered by large and fast disturbances in the current, voltage and frequency. Current saturation could be implemented within the control structure for device protection from over-currents. Insight on how the wind turbine fully rated frequency converters and controllers may interact with the VSC-HVDC converter station is also discussed.