The development of high power density power converters has become an important topic in power electronics because of increasing demand in transportation applications including marine, aviation and vehicle system. The possibility for greater power densities due to absence of a DC link is made matrix converter topologies more attractive for these applications. Additionally, with the emerging SiC device technology, the operating switching frequency and temperature of the converter can be potentially increased. The extended switching frequency and temperature range provide opportunities to further improve the power density of the power converters. The aim of this thesis is to understand how SiC devices are different from the conventional Si devices and the effect these differences have on the design and performance of a matrix converter. Specific gate drive circuits are designed and implemented to fully utilize the high speed switching capabilities of these emerging semiconductor devices. A method to evaluate the conduction and switching losses and performance of Si and SiC power devices in the matrix converter circuit is developed. The developed method is used to compare power losses of matrix converters designed with different Si and SiC devices for a range of operating temperatures and switching frequencies. A design procedure for matrix converter input filters is proposed to fulfil power quality standard requirements and maximize the filter power density. The impact of the switching frequency on the input filter volume has also been considered in this work. The output waveform distortion due to commutation time in high switching frequency SiC matrix converters is also investigated and a three-step current commutation strategy is used to minimize the problem. Finally the influence of parasitic inductance on the behaviour of SiC power MOSFET matrix converters is investigated to highlight the challenges of high speed power devices.

The work presented in this thesis aims to improve the performance of the Fundamental PWM sensorless control technique by proposing a new way to estimate current derivatives in the presence of high frequency oscillations. The Fundamental PWM technique offers performance across the entire speed range (including zero speed). The method requires current derivative measurements when certain PWM (Pulse Width Modulation) active and null vectors are applied to the machine. However the switching action of the active devices in the inverter and the associated large dv/dt result in current and current derivative waveforms being affected by high frequency oscillations which prevent accurate measurement of the current derivative. Other approaches have allowed these oscillations to decay before attempting to take a derivative measurement. This requires that the PWM vectors are applied to the machine for a time sufficient to allow the oscillations to decay and a derivative measurement to be made (the minimum pulse width). On some occasions this time is longer than the time a vector would have normally been applied for (for example when operating at low speed) and the vectors must be extended and later compensated. Vector extension introduces undesirable current distortion, audible noise, torque ripple and vibration. In this thesis the high frequency oscillations and their sources are investigated and a method of using Artificial Neural Networks to estimate current derivatives using only a short window of the transient current response is proposed. The method is able to estimate the derivative directly from phase current measurements affected by high frequency oscillations and thus allows a reduction in the minimum pulse width to be achieved (since it is no longer necessary to wait for the oscillations to fully decay) without the need for dedicated current derivative sensors. The performance of the technique is validated with experimental results.

Multilevel converters have received significant interest recently as a result of their high power capability and good power quality. However due to the large number of sensitive components including power semiconductor devices and capacitors used in such circuits there is a high likelihood of component failures. This thesis considers one of the most promising multilevel topologies---the modular multilevel converter (MMC). Several methods are presented to detect and locate open-circuit faults in the power semiconductor devices in an MMC. These methods are based on sliding mode observers (SMOs). The signals used in the proposed methods are already available as measurement inputs to the control system and no additional measurement elements are required. An experimental MMC rig has been designed and built to validate these fault detection and isolation methods. The methods can be used with other multilevel converter topologies employing similar analysis and principles.

Over the last few years, the non-volatile memories (NVM) have been dominating the research of the storage elements. The resistance random-access memory (RRAM) and the memristor that employs the resistive switching (RS) mechanism appear to be potential candidates for NVM. Among the RS materials that were reported is the TaOx which showed surprising RS performance. This oxide material has been widely used to construct a metal-insulator-semiconductor-metal (MISM) RRAM which can be referred to as bi-layered RRAM. This bi-layered RRAM consists of TaOx as a bulk material and Ta2O5 as an insulator layer, sandwiched between two platinum electrodes to form Pt/Ta2O5/TaOx/Pt RRAM. However, a physics-based mathematical model of this RRAM is required to further study the detailed physics behind its conduction mechanism and the RS process. In addition to the mathematical model, a SPICE model is also required to understand the behaviour of this bi-layered RRAM device when integrated in memory design for the future generation storage devices or when used in RRAM-based circuit applications. This doctoral research presents novel mathematical and SPICE models of a bipolar resistive switching (BRS) of the Pt/Ta2O5/TaOx/Pt bi-layered RRAM. For this purpose, MATLAB and LTSPICE are used to design the mathematical and the SPICE bi-layered RRAM models, respectively, and the obtained simulation results for both models are compared with the experimental data from SAMSUNG labs. The novelty of the mathematical model lies in incorporating the tunnelling probability factor (TPF) between the semiconductor and the metal layers and therefore, demonstrating its effect on the conduction mechanism. In addition, the effect of continuous variation of the interface traps densities and the ideality factor during BRS is modelled using the semiconductor properties and the characteristics of the metal-insulator-semiconductor (MIS) system. Thus, the model emphasizes the dependency of the device current on the physical characteristics of the insulator layer. Moreover, the electric field equation for the active region is derived for the MISM structure which is used together with Mott and Gurney rigid point-ion model and Joule heating effect to model the oxygen ion migration mechanism. Finally, the model also demonstrates the self-limiting growth of the doped region. The proposed SPICE model emphasizes the impact of the change in the switching layer thickness on the device behaviour at low resistance state (LRS), high resistance state (HRS), and the transitional period. The validity of the SPICE model is verified through using three different sets of experimental data from Pt/Ta2O5/TaOx/Pt RRAM with switching layer thickness smaller than 5 nm. The SPICE model reproduced all the major features from the experimental results for the SET and RESET processes and also the asymmetric and the symmetric characteristics in HRS and LRS, respectively. The SPICE model matches the measured experimental results with an average error of < 11%. It also showed stable behaviour for its HRS and LRS regions under different types of input signals. The model is parameterized in order to fit into Ta2O5/TaOx RRAM devices with switching layer thickness smaller than 5 nm, thus, facilitating the model usage. The SPICE model can be included in the SPICE-compatible circuit simulation and is suitable for the exploration of the Ta2O5/TaOx bi-layered RRAM device performance at circuit level. At the end of the research, a metal-insulator-metal (MIM) RRAM SPICE model of Ta/TaOx/Pt is developed which can be used in the future work to compare between the MISM and MIM TaOx-based RRAM devices.

Motion capture is the process of measuring and subsequently reconstructing the movement of an animated object or being in virtual space. Virtual reconstructions of human motion play an important role in numerous application areas such as animation, medical science, ergonomics, etc. While optical motion capture systems are the industry standard, inertial body sensor networks are becoming viable alternatives due to portability, practicality and cost. This thesis presents an innovative inertial motion capture framework for constructing body sensor networks through software environments, smartphones and web technologies. The first component of the framework is a unique inertial motion capture software environment aimed at providing an improved experimentation environment, accompanied by programming scaffolding and a driver development kit, for users interested in studying or engineering body sensor networks. The software environment provides a bespoke 3D engine for kinematic motion visualisations and a set of tools for hardware integration. The software environment is used to develop the hardware behind a prototype motion capture suit focused on low-power consumption and hardware-centricity. Additional inertial measurement units, which are available commercially, are also integrated to demonstrate the functionality the software environment while providing the framework with additional sources for motion data. The smartphone is the most ubiquitous computing technology and its worldwide uptake has prompted many advances in wearable inertial sensing technologies. Smartphones contain gyroscopes, accelerometers and magnetometers, a combination of sensors that is commonly found in inertial measurement units. This thesis presents a mobile application that investigates whether the smartphone is capable of inertial motion capture by constructing a novel omnidirectional body sensor network. This thesis proposes a novel use for web technologies through the development of the Motion Cloud, a repository and gateway for inertial data. Web technologies have the potential to replace motion capture file formats with online repositories and to set a new standard for how motion data is stored. From a single inertial measurement unit to a more complex body sensor network, the proposed architecture is extendable and facilitates the integration of any inertial hardware configuration. The Motion Cloud's data can be accessed through an application-programming interface or through a web portal that provides users with the functionality for visualising and exporting the motion data.

The two-stage AC to AC direct power converter is an alternative matrix converter topology, which offers the benefits of sinusoidal input currents and output voltages, bidirectional power flow and controllable input power factor. The absence of any energy storage devices, such as electrolytic capacitors, has increased the potential lifetime of the converter. In this research work, a new multi-motor drive system based on a two-stage direct power converter has been proposed, with two motors connected on the same shaft. A vector control scheme is proposed where each motor has an independent current control loop, but shares a single speed control loop. The two-motor on the same shaft solution has applications in aerospace to increase the availability of the system. The two-stage direct power converter therefore offers the possibility of a cost effective multi-motor drive system. The feasibility and performance of the proposed multi-motor drive system is demonstrated through simulation results and validated with experimental results from a laboratory prototype.

Microstrip patch antenna is used extensively in wireless and mobile applications due to its low-profile and lightweight. However, this antenna is prone to low gain, limited bandwidth and increased cross polarization levels. Electromagnetic Bandgap (EBG) structures are able to enhance the performance of this type of antenna. In this work, the performance of the patch antenna when integrated with EBG structure is investigated. A preliminary simulation study on the performance of a microstrip patch antenna integrated with Electromagnetic Bandgap (EBG) structures, indicated improvement in the radiation characteristics. First, the EBG characterization effort is undertaken. The bandgap of complementary and non-complementary form of five geometries are analyzed using the transmission line method. The analysis through simulation and measurement, show that complementary form sees a significant shift in the bandgap to lower frequencies and offer wider bandgap when compared to non-complementary form. Subsequently, gain performance of a square patch antenna when it is enclosed by complementary forms of either circular or square EBG cells are investigated. It emerges that the use of complementary EBG cells results in a comparatively better gain performance. The study includes a consideration of the groundplane size and the number of rows surrounding the patch, as these could affect the gain performance. This is followed by experimental measurements to substantiate the simulation outcome. Finally, the gain performance of a wideband antenna when it is configured with an EBG structure which functions as a reflector, also known as Artificial Magnetic Conductor (AMC) is investigated and reported. Four variations of the AMC structure are investigated i.e. a square cell backed by square cells (with and without vias) and square cells backed by a PEC (with and without vias). The properties of gain, impedance bandwidth and power patterns are measured and reported over the wideband frequencies of 3-10GHz.

In this thesis the author presents a new method for the location, extraction and normalisation of discrete objects found in digital images. The extraction is by means of sub-pixcel contour following around the object. The normalisation obtains and removes the information concerning size, orientation and location of the object within an image. Analyses of the results are carried out to determine the confidence in recognition of patterns, and methods of cross correlation of object descriptions using Fourier transforms are demonstrated.

Modelling detailed electromagnetic interactions in Electromagnetic Compatibility predictions is an extremely demanding task, made more difficult by the increasing complexity of modem engineering problems. Over the last decade major innovations in numerical models and methods have been introduced to reduce demands on computational resources or render the simulations of large systems containing a diverse range of physical features possible. This thesis presents one of the methods of dealing with large systems which utilises the concept of sub-cells containing fine geometrical objects. A general approach to embedding fine features into a coarse numerical time-domain techniques such as the Transmission Line Modelling (TLM) method is proposed. A non-standard node has been developed that mimics the electro- magnetic behaviour of virtually any object or group of small objects wholly or partially enclosed by a volume of space represented by the numerical cell. The core of this scheme is to identify a suitable set of local field solutions to Maxwell's equations within the vicinity of the enclosed objects and, by correctly sampling the fields on the boundary of the cell, to integrate these with field solutions represented by the neighbouring nodes, ensuring both field continuity and power conservation. The idea whilst simple leads to an algorithm that is both explicitly stable and conservative as well as only incurring a minor computational overhead compared to a conventional TLM algorithm. It is noted that, as the required identification and evaluation of the local field solutions occurs as a pre-processing stage prior to the main TLM run and that the non-standard nodes are a small proportion of the coarse grid, a significant overall reduction in computational requirements is achieved in comparison to direct fine meshing of the features. Another advantage of this approach lies in the fact that the local solutions to Maxwell's equations calculated in the pre-run process can be obtained by any suitable means. Analytical formulations, numerical results of another simulation or simply experimental measurements are some of the possibilities. The approach is employed to investigate a variety of EMC problems. An analysis of the field scattered from multiple cylindrical geometries embedded within a single two-dimensional cell is presented. Multiple conducting and lossy wires, dielectric rods and dielectric coated wires, conducting strips and slots are also studied. Three-dimensional simulations are shown for an arbitrarily orientated wires, small dielectric and conducting spheres and other canonical shapes. The approach is also successfully applied to other disciplines where modelling plays an important role. The flexibility of the algorithm is demonstrated for simulations of photonic structures with the primary focus placed upon photonic band-gap materials.

Advanced power electronics systems are increasingly being used for AC motor drives, due to their numerous advantages in terms of performance and flexibility; however, due to their switching behaviour, they introduce significant harmonic content. To reduce any interaction with other appliances suitable EMI filters need to be designed and implemented. The focus of this thesis is on the characterization of a matrix converter induction motor drive for aerospace application from the point of view of EMI interference and on the design and implementation of suitable filtering systems. Concerns about Electro Magnetic Interferences are particularly justified in the light of the fact that high reliability is sought after in such applications. The main interest in this work lies in the electromagnetic regulations defining the allowable conducted emissions in the frequencies between 150 kHz and 30 MHz. The first goal achieved by this work is to characterize the EMI signature of a matrix converter induction motor drive using common and differential mode measurements of the converter and motor impedances separately. Based only on these measurements the project aims to synthesize accurate HF models for the Induction Motor and the Matrix Converter in common and differential mode, without the need of deep level studies that may involve long Finite Elements (FE) simulations of the physical system characteristics. This thesis proposes two general novel HF models for Matrix Converters and Induction Motors that could also be applied in any other application or operating condition. These models are automatically tuned and optimized by a suitably developed Genetic Algorithm (GA) routine capable to match those models with real experimental measurements. This thesis reports the methodologies used for both input and output filter design, together with description and analysis of some issues encountered during the process.